[all] Replace Result<T> with optional<T> plus out Error parameter

36 files changed, 550 insertions, 486 deletions

diff --git a/benchmark/parse/filter.benchmark.cpp b/benchmark/parse/filter.benchmark.cpp
index 3918f03539..d650cb72c9 100644
--- a/benchmark/parse/filter.benchmark.cpp
+++ b/benchmark/parse/filter.benchmark.cpp
@@ -14,7 +14,8 @@ using namespace mbgl;
 style::Filter parse(const char* expression) {
     rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> doc;
     doc.Parse<0>(expression);
-    return *style::conversion::convert<style::Filter, JSValue>(doc);
+    style::conversion::Error error;
+    return *style::conversion::convert<style::Filter, JSValue>(doc, error);
 }
 
 static void Parse_Filter(benchmark::State& state) {
diff --git a/cmake/core-files.cmake b/cmake/core-files.cmake
index 45a3ed25b3..e98f999116 100644
--- a/cmake/core-files.cmake
+++ b/cmake/core-files.cmake
@@ -276,8 +276,6 @@ set(MBGL_CORE_FILES
     src/mbgl/style/possibly_evaluated_property_value.hpp
     src/mbgl/style/property_evaluation_parameters.hpp
     src/mbgl/style/property_evaluator.hpp
-    src/mbgl/style/property_parsing.cpp
-    src/mbgl/style/property_parsing.hpp
     src/mbgl/style/rapidjson_conversion.hpp
     src/mbgl/style/source.cpp
     src/mbgl/style/source_impl.cpp
diff --git a/include/mbgl/style/conversion.hpp b/include/mbgl/style/conversion.hpp
index e53adcb942..d6fb3a6dd0 100644
--- a/include/mbgl/style/conversion.hpp
+++ b/include/mbgl/style/conversion.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <mbgl/util/variant.hpp>
+#include <mbgl/util/optional.hpp>
 
 #include <string>
 
@@ -21,11 +21,11 @@ namespace conversion {
    A single template function serves as the public interface:
 
        template <class T, class V>
-       Result<T> convert(const V& value);
+       optional<T> convert(const V& value, Error& error);
 
-   Where `T` is one of the above types. If the conversion fails, the `Error` variant of `Result` is
-   returned, which includes diagnostic text suitable for presentation to a library user. Otherwise,
-   the `T` variant of `Result` is returned.
+   Where `T` is one of the above types. If the conversion fails, the result is empty, and the
+   error parameter includes diagnostic text suitable for presentation to a library user. Otherwise,
+   a filled optional is returned.
 
    The implementation of `convert` requires that the following are legal expressions for a value `v`
    of type `const V&`:
@@ -57,37 +57,12 @@ namespace conversion {
 
 struct Error { std::string message; };
 
-template <class T>
-class Result : private variant<T, Error> {
-public:
-    using variant<T, Error>::variant;
-
-    explicit operator bool() const {
-        return this->template is<T>();
-    }
-
-    T& operator*() {
-        assert(this->template is<T>());
-        return this->template get<T>();
-    }
-
-    const T& operator*() const {
-        assert(this->template is<T>());
-        return this->template get<T>();
-    }
-
-    const Error& error() const {
-        assert(this->template is<Error>());
-        return this->template get<Error>();
-    }
-};
-
 template <class T, class Enable = void>
 struct Converter;
 
 template <class T, class V, class...Args>
-Result<T> convert(const V& value, Args&&...args) {
-    return Converter<T>()(value, std::forward<Args>(args)...);
+optional<T> convert(const V& value, Error& error, Args&&...args) {
+    return Converter<T>()(value, error, std::forward<Args>(args)...);
 }
 
 } // namespace conversion
diff --git a/include/mbgl/style/conversion/constant.hpp b/include/mbgl/style/conversion/constant.hpp
index 05bf968f4d..1e1fdc2ee8 100644
--- a/include/mbgl/style/conversion/constant.hpp
+++ b/include/mbgl/style/conversion/constant.hpp
@@ -16,10 +16,11 @@ namespace conversion {
 template <>
 struct Converter<bool> {
     template <class V>
-    Result<bool> operator()(const V& value) const {
+    optional<bool> operator()(const V& value, Error& error) const {
         optional<bool> converted = toBool(value);
         if (!converted) {
-            return Error { "value must be a boolean" };
+            error = { "value must be a boolean" };
+            return {};
         }
         return *converted;
     }
@@ -28,10 +29,11 @@ struct Converter<bool> {
 template <>
 struct Converter<float> {
     template <class V>
-    Result<float> operator()(const V& value) const {
+    optional<float> operator()(const V& value, Error& error) const {
         optional<float> converted = toNumber(value);
         if (!converted) {
-            return Error { "value must be a number" };
+            error = { "value must be a number" };
+            return {};
         }
         return *converted;
     }
@@ -40,10 +42,11 @@ struct Converter<float> {
 template <>
 struct Converter<std::string> {
     template <class V>
-    Result<std::string> operator()(const V& value) const {
+    optional<std::string> operator()(const V& value, Error& error) const {
         optional<std::string> converted = toString(value);
         if (!converted) {
-            return Error { "value must be a string" };
+            error = { "value must be a string" };
+            return {};
         }
         return *converted;
     }
@@ -52,15 +55,17 @@ struct Converter<std::string> {
 template <class T>
 struct Converter<T, typename std::enable_if_t<std::is_enum<T>::value>> {
     template <class V>
-    Result<T> operator()(const V& value) const {
+    optional<T> operator()(const V& value, Error& error) const {
         optional<std::string> string = toString(value);
         if (!string) {
-            return Error { "value must be a string" };
+            error = { "value must be a string" };
+            return {};
         }
 
         const auto result = Enum<T>::toEnum(*string);
         if (!result) {
-            return Error { "value must be a valid enumeration value" };
+            error = { "value must be a valid enumeration value" };
+            return {};
         }
 
         return *result;
@@ -70,15 +75,17 @@ struct Converter<T, typename std::enable_if_t<std::is_enum<T>::value>> {
 template <>
 struct Converter<Color> {
     template <class V>
-    Result<Color> operator()(const V& value) const {
+    optional<Color> operator()(const V& value, Error& error) const {
         optional<std::string> string = toString(value);
         if (!string) {
-            return Error { "value must be a string" };
+            error = { "value must be a string" };
+            return {};
         }
 
         optional<Color> color = Color::parse(*string);
         if (!color) {
-            return Error { "value must be a valid color" };
+            error = { "value must be a valid color" };
+            return {};
         }
 
         return *color;
@@ -88,15 +95,17 @@ struct Converter<Color> {
 template <>
 struct Converter<std::array<float, 2>> {
     template <class V>
-    Result<std::array<float, 2>> operator()(const V& value) const {
+    optional<std::array<float, 2>> operator()(const V& value, Error& error) const {
         if (!isArray(value) || arrayLength(value) != 2) {
-            return Error { "value must be an array of two numbers" };
+            error = { "value must be an array of two numbers" };
+            return {};
         }
 
         optional<float> first = toNumber(arrayMember(value, 0));
         optional<float> second = toNumber(arrayMember(value, 1));
         if (!first || !second) {
-            return Error { "value must be an array of two numbers" };
+            error = { "value must be an array of two numbers" };
+            return {};
         }
 
         return std::array<float, 2> {{ *first, *second }};
@@ -106,9 +115,10 @@ struct Converter<std::array<float, 2>> {
 template <>
 struct Converter<std::array<float, 4>> {
     template <class V>
-    Result<std::array<float, 4>> operator()(const V& value) const {
+    optional<std::array<float, 4>> operator()(const V& value, Error& error) const {
         if (!isArray(value) || arrayLength(value) != 4) {
-            return Error { "value must be an array of four numbers" };
+            error = { "value must be an array of four numbers" };
+            return {};
         }
 
         optional<float> first = toNumber(arrayMember(value, 0));
@@ -116,7 +126,8 @@ struct Converter<std::array<float, 4>> {
         optional<float> third = toNumber(arrayMember(value, 2));
         optional<float> fourth = toNumber(arrayMember(value, 3));
         if (!first || !second) {
-            return Error { "value must be an array of four numbers" };
+            error = { "value must be an array of four numbers" };
+            return {};
         }
 
         return std::array<float, 4> {{ *first, *second, *third, *fourth }};
@@ -126,9 +137,10 @@ struct Converter<std::array<float, 4>> {
 template <>
 struct Converter<std::vector<float>> {
     template <class V>
-    Result<std::vector<float>> operator()(const V& value) const {
+    optional<std::vector<float>> operator()(const V& value, Error& error) const {
         if (!isArray(value)) {
-            return Error { "value must be an array" };
+            error = { "value must be an array" };
+            return {};
         }
 
         std::vector<float> result;
@@ -137,7 +149,8 @@ struct Converter<std::vector<float>> {
         for (std::size_t i = 0; i < arrayLength(value); ++i) {
             optional<float> number = toNumber(arrayMember(value, i));
             if (!number) {
-                return Error { "value must be an array of numbers" };
+                error = { "value must be an array of numbers" };
+                return {};
             }
             result.push_back(*number);
         }
@@ -149,9 +162,10 @@ struct Converter<std::vector<float>> {
 template <>
 struct Converter<std::vector<std::string>> {
     template <class V>
-    Result<std::vector<std::string>> operator()(const V& value) const {
+    optional<std::vector<std::string>> operator()(const V& value, Error& error) const {
         if (!isArray(value)) {
-            return Error { "value must be an array" };
+            error = { "value must be an array" };
+            return {};
         }
 
         std::vector<std::string> result;
@@ -160,7 +174,8 @@ struct Converter<std::vector<std::string>> {
         for (std::size_t i = 0; i < arrayLength(value); ++i) {
             optional<std::string> string = toString(arrayMember(value, i));
             if (!string) {
-                return Error { "value must be an array of strings" };
+                error = { "value must be an array of strings" };
+                return {};
             }
             result.push_back(*string);
         }
diff --git a/include/mbgl/style/conversion/data_driven_property_value.hpp b/include/mbgl/style/conversion/data_driven_property_value.hpp
index 83f44fdb27..79b15dcfb0 100644
--- a/include/mbgl/style/conversion/data_driven_property_value.hpp
+++ b/include/mbgl/style/conversion/data_driven_property_value.hpp
@@ -12,29 +12,29 @@ namespace conversion {
 template <class T>
 struct Converter<DataDrivenPropertyValue<T>> {
     template <class V>
-    Result<DataDrivenPropertyValue<T>> operator()(const V& value) const {
+    optional<DataDrivenPropertyValue<T>> operator()(const V& value, Error& error) const {
         if (isUndefined(value)) {
-            return {};
+            return DataDrivenPropertyValue<T>();
         } else if (!isObject(value)) {
-            Result<T> constant = convert<T>(value);
+            optional<T> constant = convert<T>(value, error);
             if (!constant) {
-                return constant.error();
+                return {};
             }
             return DataDrivenPropertyValue<T>(*constant);
         } else if (!objectMember(value, "property")) {
-            Result<CameraFunction<T>> function = convert<CameraFunction<T>>(value);
+            optional<CameraFunction<T>> function = convert<CameraFunction<T>>(value, error);
             if (!function) {
-                return function.error();
+                return {};
             }
             return DataDrivenPropertyValue<T>(*function);
         } else {
-            Result<CompositeFunction<T>> composite = convert<CompositeFunction<T>>(value);
+            optional<CompositeFunction<T>> composite = convert<CompositeFunction<T>>(value, error);
             if (composite) {
                 return DataDrivenPropertyValue<T>(*composite);
             }
-            Result<SourceFunction<T>> source = convert<SourceFunction<T>>(value);
+            optional<SourceFunction<T>> source = convert<SourceFunction<T>>(value, error);
             if (!source) {
-                return source.error();
+                return {};
             }
             return DataDrivenPropertyValue<T>(*source);
         }
diff --git a/include/mbgl/style/conversion/filter.hpp b/include/mbgl/style/conversion/filter.hpp
index 2c4eeb4ac7..1f8f0fd161 100644
--- a/include/mbgl/style/conversion/filter.hpp
+++ b/include/mbgl/style/conversion/filter.hpp
@@ -12,65 +12,71 @@ template <>
 struct Converter<Filter> {
 public:
     template <class V>
-    Result<Filter> operator()(const V& value) const {
+    optional<Filter> operator()(const V& value, Error& error) const {
         if (!isArray(value)) {
-            return Error { "filter expression must be an array" };
+            error = { "filter expression must be an array" };
+            return {};
         }
 
         if (arrayLength(value) < 1) {
-            return Error { "filter expression must have at least 1 element" };
+            error = { "filter expression must have at least 1 element" };
+            return {};
         }
 
         optional<std::string> op = toString(arrayMember(value, 0));
         if (!op) {
-            return Error { "filter operator must be a string" };
+            error = { "filter operator must be a string" };
+            return {};
         }
 
         if (*op == "==") {
-            return convertEqualityFilter<EqualsFilter, TypeEqualsFilter, IdentifierEqualsFilter>(value);
+            return convertEqualityFilter<EqualsFilter, TypeEqualsFilter, IdentifierEqualsFilter>(value, error);
         } else if (*op == "!=") {
-            return convertEqualityFilter<NotEqualsFilter, TypeNotEqualsFilter, IdentifierNotEqualsFilter>(value);
+            return convertEqualityFilter<NotEqualsFilter, TypeNotEqualsFilter, IdentifierNotEqualsFilter>(value, error);
         } else if (*op == ">") {
-            return convertBinaryFilter<GreaterThanFilter>(value);
+            return convertBinaryFilter<GreaterThanFilter>(value, error);
         } else if (*op == ">=") {
-            return convertBinaryFilter<GreaterThanEqualsFilter>(value);
+            return convertBinaryFilter<GreaterThanEqualsFilter>(value, error);
         } else if (*op == "<") {
-            return convertBinaryFilter<LessThanFilter>(value);
+            return convertBinaryFilter<LessThanFilter>(value, error);
         } else if (*op == "<=") {
-            return convertBinaryFilter<LessThanEqualsFilter>(value);
+            return convertBinaryFilter<LessThanEqualsFilter>(value, error);
         } else if (*op == "in") {
-            return convertSetFilter<InFilter, TypeInFilter, IdentifierInFilter>(value);
+            return convertSetFilter<InFilter, TypeInFilter, IdentifierInFilter>(value, error);
         } else if (*op == "!in") {
-            return convertSetFilter<NotInFilter, TypeNotInFilter, IdentifierNotInFilter>(value);
+            return convertSetFilter<NotInFilter, TypeNotInFilter, IdentifierNotInFilter>(value, error);
         } else if (*op == "all") {
-            return convertCompoundFilter<AllFilter>(value);
+            return convertCompoundFilter<AllFilter>(value, error);
         } else if (*op == "any") {
-            return convertCompoundFilter<AnyFilter>(value);
+            return convertCompoundFilter<AnyFilter>(value, error);
         } else if (*op == "none") {
-            return convertCompoundFilter<NoneFilter>(value);
+            return convertCompoundFilter<NoneFilter>(value, error);
         } else if (*op == "has") {
-            return convertUnaryFilter<HasFilter, HasIdentifierFilter>(value);
+            return convertUnaryFilter<HasFilter, HasIdentifierFilter>(value, error);
         } else if (*op == "!has") {
-           return convertUnaryFilter<NotHasFilter, NotHasIdentifierFilter>(value);
+           return convertUnaryFilter<NotHasFilter, NotHasIdentifierFilter>(value, error);
         }
 
-        return Error { "filter operator must be one of \"==\", \"!=\", \">\", \">=\", \"<\", \"<=\", \"in\", \"!in\", \"all\", \"any\", \"none\", \"has\", or \"!has\"" };
+        error = { "filter operator must be one of \"==\", \"!=\", \">\", \">=\", \"<\", \"<=\", \"in\", \"!in\", \"all\", \"any\", \"none\", \"has\", or \"!has\"" };
+        return {};
     }
 
 private:
-    Result<Value> normalizeValue(const optional<Value>& value) const {
+    optional<Value> normalizeValue(const optional<Value>& value, Error& error) const {
         if (!value) {
-            return Error { "filter expression value must be a boolean, number, or string" };
+            error = { "filter expression value must be a boolean, number, or string" };
+            return {};
         } else {
             return *value;
         }
     }
 
     template <class V>
-    Result<FeatureType> toFeatureType(const V& value) const {
+    optional<FeatureType> toFeatureType(const V& value, Error& error) const {
         optional<std::string> type = toString(value);
         if (!type) {
-            return Error { "value for $type filter must be a string" };
+            error = { "value for $type filter must be a string" };
+            return {};
         } else if (*type == "Point") {
             return FeatureType::Point;
         } else if (*type == "LineString") {
@@ -78,162 +84,173 @@ private:
         } else if (*type == "Polygon") {
             return FeatureType::Polygon;
         } else {
-            return Error { "value for $type filter must be Point, LineString, or Polygon" };
+            error = { "value for $type filter must be Point, LineString, or Polygon" };
+            return {};
         }
     }
 
     template <class V>
-    Result<FeatureIdentifier> toFeatureIdentifier(const V& value) const {
+    optional<FeatureIdentifier> toFeatureIdentifier(const V& value, Error& error) const {
         optional<Value> identifier = toValue(value);
         if (!identifier) {
-            return Error { "filter expression value must be a boolean, number, or string" };
+            error = { "filter expression value must be a boolean, number, or string" };
+            return {};
         } else {
             return (*identifier).match(
-                [] (uint64_t t) -> Result<FeatureIdentifier> { return t; },
-                [] ( int64_t t) -> Result<FeatureIdentifier> { return t; },
-                [] (  double t) -> Result<FeatureIdentifier> { return t; },
-                [] (const std::string& t) -> Result<FeatureIdentifier> { return t; },
-                [] (const auto&) -> Result<FeatureIdentifier> {
-                    return Error { "filter expression value must be a boolean, number, or string" };
+                [] (uint64_t t) -> optional<FeatureIdentifier> { return { t }; },
+                [] ( int64_t t) -> optional<FeatureIdentifier> { return { t }; },
+                [] (  double t) -> optional<FeatureIdentifier> { return { t }; },
+                [] (const std::string& t) -> optional<FeatureIdentifier> { return { t }; },
+                [&] (const auto&) -> optional<FeatureIdentifier> {
+                    error = { "filter expression value must be a boolean, number, or string" };
+                    return {};
                 });
         }
     }
 
     template <class FilterType, class IdentifierFilterType, class V>
-    Result<Filter> convertUnaryFilter(const V& value) const {
+    optional<Filter> convertUnaryFilter(const V& value, Error& error) const {
         if (arrayLength(value) < 2) {
-            return Error { "filter expression must have 2 elements" };
+            error = { "filter expression must have 2 elements" };
+            return {};
         }
 
         optional<std::string> key = toString(arrayMember(value, 1));
         if (!key) {
-            return Error { "filter expression key must be a string" };
+            error = { "filter expression key must be a string" };
+            return {};
         }
 
         if (*key == "$id") {
-            return IdentifierFilterType {};
+            return { IdentifierFilterType {} };
         } else {
-            return FilterType { *key };
+            return { FilterType { *key } };
         }
     }
 
     template <class FilterType, class TypeFilterType, class IdentifierFilterType, class V>
-    Result<Filter> convertEqualityFilter(const V& value) const {
+    optional<Filter> convertEqualityFilter(const V& value, Error& error) const {
         if (arrayLength(value) < 3) {
-            return Error { "filter expression must have 3 elements" };
+            error = { "filter expression must have 3 elements" };
+            return {};
         }
 
         optional<std::string> key = toString(arrayMember(value, 1));
         if (!key) {
-            return Error { "filter expression key must be a string" };
+            error = { "filter expression key must be a string" };
+            return {};
         }
 
         if (*key == "$type") {
-            Result<FeatureType> filterValue = toFeatureType(arrayMember(value, 2));
+            optional<FeatureType> filterValue = toFeatureType(arrayMember(value, 2), error);
             if (!filterValue) {
-                return filterValue.error();
+                return {};
             }
 
-            return TypeFilterType { *filterValue };
+            return { TypeFilterType { *filterValue } };
 
         } else if (*key == "$id") {
-            Result<FeatureIdentifier> filterValue = toFeatureIdentifier(arrayMember(value, 2));
+            optional<FeatureIdentifier> filterValue = toFeatureIdentifier(arrayMember(value, 2), error);
             if (!filterValue) {
-                return filterValue.error();
+                return {};
             }
 
-            return IdentifierFilterType { *filterValue };
+            return { IdentifierFilterType { *filterValue } };
 
         } else {
-            Result<Value> filterValue = normalizeValue(toValue(arrayMember(value, 2)));
+            optional<Value> filterValue = normalizeValue(toValue(arrayMember(value, 2)), error);
             if (!filterValue) {
-                return filterValue.error();
+                return {};
             }
 
-            return FilterType { *key, *filterValue };
+            return { FilterType { *key, *filterValue } };
         }
     }
 
     template <class FilterType, class V>
-    Result<Filter> convertBinaryFilter(const V& value) const {
+    optional<Filter> convertBinaryFilter(const V& value, Error& error) const {
         if (arrayLength(value) < 3) {
-            return Error { "filter expression must have 3 elements" };
+            error = { "filter expression must have 3 elements" };
+            return {};
         }
 
         optional<std::string> key = toString(arrayMember(value, 1));
         if (!key) {
-            return Error { "filter expression key must be a string" };
+            error = { "filter expression key must be a string" };
+            return {};
         }
 
-        Result<Value> filterValue = normalizeValue(toValue(arrayMember(value, 2)));
+        optional<Value> filterValue = normalizeValue(toValue(arrayMember(value, 2)), error);
         if (!filterValue) {
-            return filterValue.error();
+            return {};
         }
 
-        return FilterType { *key, *filterValue };
+        return { FilterType { *key, *filterValue } };
     }
 
     template <class FilterType, class TypeFilterType, class IdentifierFilterType, class V>
-    Result<Filter> convertSetFilter(const V& value) const {
+    optional<Filter> convertSetFilter(const V& value, Error& error) const {
         if (arrayLength(value) < 2) {
-            return Error { "filter expression must at least 2 elements" };
+            error = { "filter expression must at least 2 elements" };
+            return {};
         }
 
         optional<std::string> key = toString(arrayMember(value, 1));
         if (!key) {
-            return Error { "filter expression key must be a string" };
+            error = { "filter expression key must be a string" };
+            return {};
         }
 
         if (*key == "$type") {
             std::vector<FeatureType> values;
             for (std::size_t i = 2; i < arrayLength(value); ++i) {
-                Result<FeatureType> filterValue = toFeatureType(arrayMember(value, i));
+                optional<FeatureType> filterValue = toFeatureType(arrayMember(value, i), error);
                 if (!filterValue) {
-                    return filterValue.error();
+                    return {};
                 }
                 values.push_back(*filterValue);
             }
 
-            return TypeFilterType { std::move(values) };
+            return { TypeFilterType { std::move(values) } };
 
         } else if (*key == "$id") {
             std::vector<FeatureIdentifier> values;
             for (std::size_t i = 2; i < arrayLength(value); ++i) {
-                Result<FeatureIdentifier> filterValue = toFeatureIdentifier(arrayMember(value, i));
+                optional<FeatureIdentifier> filterValue = toFeatureIdentifier(arrayMember(value, i), error);
                 if (!filterValue) {
-                    return filterValue.error();
+                    return {};
                 }
                 values.push_back(*filterValue);
             }
 
-            return IdentifierFilterType { std::move(values) };
+            return { IdentifierFilterType { std::move(values) } };
 
         } else {
             std::vector<Value> values;
             for (std::size_t i = 2; i < arrayLength(value); ++i) {
-                Result<Value> filterValue = normalizeValue(toValue(arrayMember(value, i)));
+                optional<Value> filterValue = normalizeValue(toValue(arrayMember(value, i)), error);
                 if (!filterValue) {
-                    return filterValue.error();
+                    return {};
                 }
                 values.push_back(*filterValue);
             }
 
-            return FilterType { *key, std::move(values) };
+            return { FilterType { *key, std::move(values) } };
         }
     }
 
     template <class FilterType, class V>
-    Result<Filter> convertCompoundFilter(const V& value) const {
+    optional<Filter> convertCompoundFilter(const V& value, Error& error) const {
         std::vector<Filter> filters;
         for (std::size_t i = 1; i < arrayLength(value); ++i) {
-            Result<Filter> element = operator()(arrayMember(value, i));
+            optional<Filter> element = operator()(arrayMember(value, i), error);
             if (!element) {
-                return element.error();
+                return {};
             }
             filters.push_back(*element);
         }
 
-        return FilterType { std::move(filters) };
+        return { FilterType { std::move(filters) } };
     }
 };
 
diff --git a/include/mbgl/style/conversion/function.hpp b/include/mbgl/style/conversion/function.hpp
index a5979e6799..fa8af1e2be 100644
--- a/include/mbgl/style/conversion/function.hpp
+++ b/include/mbgl/style/conversion/function.hpp
@@ -12,18 +12,21 @@ namespace style {
 namespace conversion {
 
 template <class D, class R, class V>
-Result<std::map<D, R>> convertStops(const V& value) {
+optional<std::map<D, R>> convertStops(const V& value, Error& error) {
     auto stopsValue = objectMember(value, "stops");
     if (!stopsValue) {
-        return Error { "function value must specify stops" };
+        error = { "function value must specify stops" };
+        return {};
     }
 
     if (!isArray(*stopsValue)) {
-        return Error { "function stops must be an array" };
+        error = { "function stops must be an array" };
+        return {};
     }
 
     if (arrayLength(*stopsValue) == 0) {
-        return Error { "function must have at least one stop" };
+        error = { "function must have at least one stop" };
+        return {};
     }
 
     std::map<D, R> stops;
@@ -31,21 +34,23 @@ Result<std::map<D, R>> convertStops(const V& value) {
         const auto& stopValue = arrayMember(*stopsValue, i);
 
         if (!isArray(stopValue)) {
-            return Error { "function stop must be an array" };
+            error = { "function stop must be an array" };
+            return {};
         }
 
         if (arrayLength(stopValue) != 2) {
-            return Error { "function stop must have two elements" };
+            error = { "function stop must have two elements" };
+            return {};
         }
 
-        Result<D> d = convert<D>(arrayMember(stopValue, 0));
+        optional<D> d = convert<D>(arrayMember(stopValue, 0), error);
         if (!d) {
-            return d.error();
+            return {};
         }
 
-        Result<R> r = convert<R>(arrayMember(stopValue, 1));
+        optional<R> r = convert<R>(arrayMember(stopValue, 1), error);
         if (!r) {
-            return r.error();
+            return {};
         }
 
         stops.emplace(*d, *r);
@@ -59,10 +64,10 @@ struct Converter<ExponentialStops<T>> {
     static constexpr const char * type = "exponential";
 
     template <class V>
-    Result<ExponentialStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<float, T>(value);
+    optional<ExponentialStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<float, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
         auto baseValue = objectMember(value, "base");
@@ -72,7 +77,8 @@ struct Converter<ExponentialStops<T>> {
 
         optional<float> base = toNumber(*baseValue);
         if (!base) {
-            return Error { "function base must be a number"};
+            error = { "function base must be a number"};
+            return {};
         }
 
         return ExponentialStops<T>(*stops, *base);
@@ -84,10 +90,10 @@ struct Converter<IntervalStops<T>> {
     static constexpr const char * type = "interval";
 
     template <class V>
-    Result<IntervalStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<float, T>(value);
+    optional<IntervalStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<float, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
         return IntervalStops<T>(*stops);
     }
@@ -96,23 +102,24 @@ struct Converter<IntervalStops<T>> {
 template <>
 struct Converter<CategoricalValue> {
     template <class V>
-    Result<CategoricalValue> operator()(const V& value) const {
+    optional<CategoricalValue> operator()(const V& value, Error& error) const {
         auto b = toBool(value);
         if (b) {
-            return *b;
+            return { *b };
         }
 
         auto n = toNumber(value);
         if (n) {
-            return int64_t(*n);
+            return { int64_t(*n) };
         }
 
         auto s = toString(value);
         if (s) {
-            return *s;
+            return { *s };
         }
 
-        return Error { "stop domain value must be a number, string, or boolean" };
+        error = { "stop domain value must be a number, string, or boolean" };
+        return {};
     }
 };
 
@@ -121,10 +128,10 @@ struct Converter<CategoricalStops<T>> {
     static constexpr const char * type = "categorical";
 
     template <class V>
-    Result<CategoricalStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<CategoricalValue, T>(value);
+    optional<CategoricalStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<CategoricalValue, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
         return CategoricalStops<T>(
             std::map<CategoricalValue, T>((*stops).begin(), (*stops).end()));
@@ -136,7 +143,7 @@ struct Converter<IdentityStops<T>> {
     static constexpr const char * type = "identity";
 
     template <class V>
-    Result<IdentityStops<T>> operator()(const V&) const {
+    optional<IdentityStops<T>> operator()(const V&, Error&) const {
         return IdentityStops<T>();
     }
 };
@@ -148,7 +155,7 @@ template <class T, class... Ts>
 struct StopsConverter<T, variant<Ts...>> {
 public:
     template <class V>
-    Result<variant<Ts...>> operator()(const V& value) const {
+    optional<variant<Ts...>> operator()(const V& value, Error& error) const {
         std::string type = util::Interpolatable<T> ? "exponential" : "interval";
 
         auto typeValue = objectMember(value, "type");
@@ -156,16 +163,18 @@ public:
             type = *toString(*typeValue);
         }
 
-        optional<Result<variant<Ts...>>> result;
+        bool matched = false;
+        optional<variant<Ts...>> result;
 
         // Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47226
         auto tryConvert = [&] (auto* tp) {
             using Stops = std::decay_t<decltype(*tp)>;
             if (type == Converter<Stops>::type) {
-                auto stops = convert<Stops>(value);
-                result = stops
-                    ? Result<variant<Ts...>>(*stops)
-                    : Result<variant<Ts...>>(stops.error());
+                matched = true;
+                optional<Stops> stops = convert<Stops>(value, error);
+                if (stops) {
+                    result = variant<Ts...>(*stops);
+                }
             }
         };
 
@@ -173,25 +182,27 @@ public:
             (tryConvert((Ts*)nullptr), 0)...
         });
 
-        if (!result) {
-            return Error { "unsupported function type" };
+        if (!matched) {
+            error = { "unsupported function type" };
+            return {};
         }
 
-        return *result;
+        return result;
     }
 };
 
 template <class T>
 struct Converter<CameraFunction<T>> {
     template <class V>
-    Result<CameraFunction<T>> operator()(const V& value) const {
+    optional<CameraFunction<T>> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "function must be an object" };
+            error = { "function must be an object" };
+            return {};
         }
 
-        auto stops = StopsConverter<T, typename CameraFunction<T>::Stops>()(value);
+        auto stops = StopsConverter<T, typename CameraFunction<T>::Stops>()(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
         return CameraFunction<T>(*stops);
@@ -199,46 +210,50 @@ struct Converter<CameraFunction<T>> {
 };
 
 template <class T, class V>
-Result<optional<T>> convertDefaultValue(const V& value) {
+optional<optional<T>> convertDefaultValue(const V& value, Error& error) {
     auto defaultValueValue = objectMember(value, "default");
     if (!defaultValueValue) {
-        return {};
+        return optional<T>();
     }
 
-    auto defaultValue = convert<T>(*defaultValueValue);
+    auto defaultValue = convert<T>(*defaultValueValue, error);
     if (!defaultValue) {
-        return Error { "wrong type for \"default\": " + defaultValue.error().message };
+        error = { "wrong type for \"default\": " + error.message };
+        return {};
     }
 
-    return *defaultValue;
+    return { *defaultValue };
 }
 
 template <class T>
 struct Converter<SourceFunction<T>> {
     template <class V>
-    Result<SourceFunction<T>> operator()(const V& value) const {
+    optional<SourceFunction<T>> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "function must be an object" };
+            error = { "function must be an object" };
+            return {};
         }
 
         auto propertyValue = objectMember(value, "property");
         if (!propertyValue) {
-            return Error { "function must specify property" };
+            error = { "function must specify property" };
+            return {};
         }
 
         auto propertyString = toString(*propertyValue);
         if (!propertyString) {
-            return Error { "function property must be a string" };
+            error = { "function property must be a string" };
+            return {};
         }
 
-        auto stops = StopsConverter<T, typename SourceFunction<T>::Stops>()(value);
+        auto stops = StopsConverter<T, typename SourceFunction<T>::Stops>()(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
-        auto defaultValue = convertDefaultValue<T>(value);
+        auto defaultValue = convertDefaultValue<T>(value, error);
         if (!defaultValue) {
-            return defaultValue.error();
+            return {};
         }
 
         return SourceFunction<T>(*propertyString, *stops, *defaultValue);
@@ -253,29 +268,32 @@ struct CompositeValue : std::pair<float, S> {
 template <class S>
 struct Converter<CompositeValue<S>> {
     template <class V>
-    Result<CompositeValue<S>> operator()(const V& value) const {
+    optional<CompositeValue<S>> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "stop must be an object" };
+            error = { "stop must be an object" };
+            return {};
         }
 
         auto zoomValue = objectMember(value, "zoom");
         if (!zoomValue) {
-            return Error { "stop must specify zoom" };
+            error = { "stop must specify zoom" };
+            return {};
         }
 
         auto propertyValue = objectMember(value, "value");
         if (!propertyValue) {
-            return Error { "stop must specify value" };
+            error = { "stop must specify value" };
+            return {};
         }
 
-        Result<float> z = convert<float>(*zoomValue);
+        optional<float> z = convert<float>(*zoomValue, error);
         if (!z) {
-            return z.error();
+            return {};
         }
 
-        Result<S> s = convert<S>(*propertyValue);
+        optional<S> s = convert<S>(*propertyValue, error);
         if (!s) {
-            return s.error();
+            return {};
         }
 
         return CompositeValue<S> { *z, *s };
@@ -287,10 +305,10 @@ struct Converter<CompositeExponentialStops<T>> {
     static constexpr const char * type = "exponential";
 
     template <class V>
-    Result<CompositeExponentialStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<CompositeValue<float>, T>(value);
+    optional<CompositeExponentialStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<CompositeValue<float>, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
         auto base = 1.0f;
@@ -313,10 +331,10 @@ struct Converter<CompositeIntervalStops<T>> {
     static constexpr const char * type = "interval";
 
     template <class V>
-    Result<CompositeIntervalStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<CompositeValue<float>, T>(value);
+    optional<CompositeIntervalStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<CompositeValue<float>, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
         std::map<float, std::map<float, T>> convertedStops;
@@ -333,10 +351,10 @@ struct Converter<CompositeCategoricalStops<T>> {
     static constexpr const char * type = "categorical";
 
     template <class V>
-    Result<CompositeCategoricalStops<T>> operator()(const V& value) const {
-        auto stops = convertStops<CompositeValue<CategoricalValue>, T>(value);
+    optional<CompositeCategoricalStops<T>> operator()(const V& value, Error& error) const {
+        auto stops = convertStops<CompositeValue<CategoricalValue>, T>(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
         std::map<float, std::map<CategoricalValue, T>> convertedStops;
@@ -351,29 +369,32 @@ struct Converter<CompositeCategoricalStops<T>> {
 template <class T>
 struct Converter<CompositeFunction<T>> {
     template <class V>
-    Result<CompositeFunction<T>> operator()(const V& value) const {
+    optional<CompositeFunction<T>> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "function must be an object" };
+            error = { "function must be an object" };
+            return {};
         }
 
         auto propertyValue = objectMember(value, "property");
         if (!propertyValue) {
-            return Error { "function must specify property" };
+            error = { "function must specify property" };
+            return {};
         }
 
         auto propertyString = toString(*propertyValue);
         if (!propertyString) {
-            return Error { "function property must be a string" };
+            error = { "function property must be a string" };
+            return {};
         }
 
-        auto stops = StopsConverter<T, typename CompositeFunction<T>::Stops>()(value);
+        auto stops = StopsConverter<T, typename CompositeFunction<T>::Stops>()(value, error);
         if (!stops) {
-            return stops.error();
+            return {};
         }
 
-        auto defaultValue = convertDefaultValue<T>(value);
+        auto defaultValue = convertDefaultValue<T>(value, error);
         if (!defaultValue) {
-            return defaultValue.error();
+            return {};
         }
 
         return CompositeFunction<T>(*propertyString, *stops, *defaultValue);
diff --git a/include/mbgl/style/conversion/geojson.hpp b/include/mbgl/style/conversion/geojson.hpp
index ba10b3ecc8..6e6e97dbc0 100644
--- a/include/mbgl/style/conversion/geojson.hpp
+++ b/include/mbgl/style/conversion/geojson.hpp
@@ -8,7 +8,7 @@ namespace style {
 namespace conversion {
 
 template <class V>
-Result<GeoJSON> convertGeoJSON(const V& value);
+optional<GeoJSON> convertGeoJSON(const V& value, Error& error);
 
 } // namespace conversion
 } // namespace style
diff --git a/include/mbgl/style/conversion/geojson_options.hpp b/include/mbgl/style/conversion/geojson_options.hpp
index 880090b402..19383d90ce 100644
--- a/include/mbgl/style/conversion/geojson_options.hpp
+++ b/include/mbgl/style/conversion/geojson_options.hpp
@@ -11,7 +11,7 @@ template <>
 struct Converter<GeoJSONOptions> {
 
     template <class V>
-    Result<GeoJSONOptions> operator()(const V& value) const {
+    optional<GeoJSONOptions> operator()(const V& value, Error& error) const {
         GeoJSONOptions options;
 
         const auto maxzoomValue = objectMember(value, "maxzoom");
@@ -19,7 +19,8 @@ struct Converter<GeoJSONOptions> {
             if (toNumber(*maxzoomValue)) {
                 options.maxzoom = static_cast<uint8_t>(*toNumber(*maxzoomValue));
             } else {
-                return Error{ "GeoJSON source maxzoom value must be a number" };
+                error = { "GeoJSON source maxzoom value must be a number" };
+                return {};
             }
         }
 
@@ -28,7 +29,8 @@ struct Converter<GeoJSONOptions> {
             if (toNumber(*bufferValue)) {
                 options.buffer = static_cast<uint16_t>(*toNumber(*bufferValue));
             } else {
-                return Error{ "GeoJSON source buffer value must be a number" };
+                error = { "GeoJSON source buffer value must be a number" };
+                return {};
             }
         }
 
@@ -37,7 +39,8 @@ struct Converter<GeoJSONOptions> {
             if (toNumber(*toleranceValue)) {
                 options.tolerance = static_cast<double>(*toNumber(*toleranceValue));
             } else {
-                return Error{ "GeoJSON source tolerance value must be a number" };
+                error = { "GeoJSON source tolerance value must be a number" };
+                return {};
             }
         }
 
@@ -46,7 +49,8 @@ struct Converter<GeoJSONOptions> {
             if (toBool(*clusterValue)) {
                 options.cluster = *toBool(*clusterValue);
             } else {
-                return Error{ "GeoJSON source cluster value must be a boolean" };
+                error = { "GeoJSON source cluster value must be a boolean" };
+                return {};
             }
         }
 
@@ -55,7 +59,8 @@ struct Converter<GeoJSONOptions> {
             if (toNumber(*clusterMaxZoomValue)) {
                 options.clusterMaxZoom = static_cast<uint8_t>(*toNumber(*clusterMaxZoomValue));
             } else {
-                return Error{ "GeoJSON source clusterMaxZoom value must be a number" };
+                error = { "GeoJSON source clusterMaxZoom value must be a number" };
+                return {};
             }
         }
 
@@ -64,7 +69,8 @@ struct Converter<GeoJSONOptions> {
             if (toNumber(*clusterRadiusValue)) {
                 options.clusterRadius = static_cast<double>(*toNumber(*clusterRadiusValue));
             } else {
-                return Error{ "GeoJSON source clusterRadius value must be a number" };
+                error = { "GeoJSON source clusterRadius value must be a number" };
+                return {};
             }
         }
 
diff --git a/include/mbgl/style/conversion/layer.hpp b/include/mbgl/style/conversion/layer.hpp
index 0539dcf9ad..efb1df8fef 100644
--- a/include/mbgl/style/conversion/layer.hpp
+++ b/include/mbgl/style/conversion/layer.hpp
@@ -58,47 +58,53 @@ template <>
 struct Converter<std::unique_ptr<Layer>> {
 public:
     template <class V>
-    Result<std::unique_ptr<Layer>> operator()(const V& value) const {
+    optional<std::unique_ptr<Layer>> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "layer must be an object" };
+            error = { "layer must be an object" };
+            return {};
         }
 
         auto idValue = objectMember(value, "id");
         if (!idValue) {
-            return Error { "layer must have an id" };
+            error = { "layer must have an id" };
+            return {};
         }
 
         optional<std::string> id = toString(*idValue);
         if (!id) {
-            return Error { "layer id must be a string" };
+            error = { "layer id must be a string" };
+            return {};
         }
 
         auto typeValue = objectMember(value, "type");
         if (!typeValue) {
-            return Error { "layer must have a type" };
+            error = { "layer must have a type" };
+            return {};
         }
 
         optional<std::string> type = toString(*typeValue);
         if (!type) {
-            return Error { "layer type must be a string" };
+            error = { "layer type must be a string" };
+            return {};
         }
 
-        Result<std::unique_ptr<Layer>> converted;
+        optional<std::unique_ptr<Layer>> converted;
 
         if (*type == "fill") {
-            converted = convertVectorLayer<FillLayer>(*id, value);
+            converted = convertVectorLayer<FillLayer>(*id, value, error);
         } else if (*type == "line") {
-            converted = convertVectorLayer<LineLayer>(*id, value);
+            converted = convertVectorLayer<LineLayer>(*id, value, error);
         } else if (*type == "circle") {
-            converted = convertVectorLayer<CircleLayer>(*id, value);
+            converted = convertVectorLayer<CircleLayer>(*id, value, error);
         } else if (*type == "symbol") {
-            converted = convertVectorLayer<SymbolLayer>(*id, value);
+            converted = convertVectorLayer<SymbolLayer>(*id, value, error);
         } else if (*type == "raster") {
-            converted = convertRasterLayer(*id, value);
+            converted = convertRasterLayer(*id, value, error);
         } else if (*type == "background") {
-            converted = convertBackgroundLayer(*id, value);
+            converted = convertBackgroundLayer(*id, value, error);
         } else {
-            return Error { "invalid layer type" };
+            error = { "invalid layer type" };
+            return {};
         }
 
         if (!converted) {
@@ -111,7 +117,8 @@ public:
         if (minzoomValue) {
             optional<float> minzoom = toNumber(*minzoomValue);
             if (!minzoom) {
-                return Error { "minzoom must be numeric" };
+                error = { "minzoom must be numeric" };
+                return {};
             }
             layer->setMinZoom(*minzoom);
         }
@@ -120,7 +127,8 @@ public:
         if (maxzoomValue) {
             optional<float> maxzoom = toNumber(*maxzoomValue);
             if (!maxzoom) {
-                return Error { "maxzoom must be numeric" };
+                error = { "maxzoom must be numeric" };
+                return {};
             }
             layer->setMaxZoom(*maxzoom);
         }
@@ -128,19 +136,22 @@ public:
         auto layoutValue = objectMember(value, "layout");
         if (layoutValue) {
             if (!isObject(*layoutValue)) {
-                return Error { "layout must be an object" };
+                error = { "layout must be an object" };
+                return {};
             }
-            optional<Error> error = eachMember(*layoutValue, [&] (const std::string& k, const V& v) {
+            optional<Error> error_ = eachMember(*layoutValue, [&] (const std::string& k, const V& v) {
                 return setLayoutProperty(*layer, k, v);
             });
-            if (error) {
-                return *error;
+            if (error_) {
+                error = *error_;
+                return {};
             }
         }
 
-        optional<Error> error = setPaintProperties(*layer, value);
-        if (error) {
-            return *error;
+        optional<Error> error_ = setPaintProperties(*layer, value);
+        if (error_) {
+            error = *error_;
+            return {};
         }
 
         return std::move(layer);
@@ -148,15 +159,17 @@ public:
 
 private:
     template <class LayerType, class V>
-    Result<std::unique_ptr<Layer>> convertVectorLayer(const std::string& id, const V& value) const {
+    optional<std::unique_ptr<Layer>> convertVectorLayer(const std::string& id, const V& value, Error& error) const {
         auto sourceValue = objectMember(value, "source");
         if (!sourceValue) {
-            return Error { "layer must have a source" };
+            error = { "layer must have a source" };
+            return {};
         }
 
         optional<std::string> source = toString(*sourceValue);
         if (!source) {
-            return Error { "layer source must be a string" };
+            error = { "layer source must be a string" };
+            return {};
         }
 
         std::unique_ptr<LayerType> layer = std::make_unique<LayerType>(id, *source);
@@ -165,41 +178,44 @@ private:
         if (sourceLayerValue) {
             optional<std::string> sourceLayer = toString(*sourceLayerValue);
             if (!sourceLayer) {
-                return Error { "layer source-layer must be a string" };
+                error = { "layer source-layer must be a string" };
+                return {};
             }
             layer->setSourceLayer(*sourceLayer);
         }
 
         auto filterValue = objectMember(value, "filter");
         if (filterValue) {
-            Result<Filter> filter = convert<Filter>(*filterValue);
+            optional<Filter> filter = convert<Filter>(*filterValue, error);
             if (!filter) {
-                return filter.error();
+                return {};
             }
             layer->setFilter(*filter);
         }
 
-        return std::move(layer);
+        return { std::move(layer) };
     }
 
     template <class V>
-    Result<std::unique_ptr<Layer>> convertRasterLayer(const std::string& id, const V& value) const {
+    optional<std::unique_ptr<Layer>> convertRasterLayer(const std::string& id, const V& value, Error& error) const {
         auto sourceValue = objectMember(value, "source");
         if (!sourceValue) {
-            return Error { "layer must have a source" };
+            error = { "layer must have a source" };
+            return {};
         }
 
         optional<std::string> source = toString(*sourceValue);
         if (!source) {
-            return Error { "layer source must be a string" };
+            error = { "layer source must be a string" };
+            return {};
         }
 
-        return std::make_unique<RasterLayer>(id, *source);
+        return { std::make_unique<RasterLayer>(id, *source) };
     }
 
     template <class V>
-    Result<std::unique_ptr<Layer>> convertBackgroundLayer(const std::string& id, const V&) const {
-        return std::make_unique<BackgroundLayer>(id);
+    optional<std::unique_ptr<Layer>> convertBackgroundLayer(const std::string& id, const V&, Error&) const {
+        return { std::make_unique<BackgroundLayer>(id) };
     }
 };
 
diff --git a/include/mbgl/style/conversion/property_setter.hpp b/include/mbgl/style/conversion/property_setter.hpp
index 51ec4778d9..1f537f3c4d 100644
--- a/include/mbgl/style/conversion/property_setter.hpp
+++ b/include/mbgl/style/conversion/property_setter.hpp
@@ -26,9 +26,10 @@ optional<Error> setLayoutProperty(Layer& layer, const V& value) {
         return Error { "layer doesn't support this property" };
     }
 
-    Result<PropertyValue> typedValue = convert<PropertyValue>(value);
+    Error error;
+    optional<PropertyValue> typedValue = convert<PropertyValue>(value, error);
     if (!typedValue) {
-        return typedValue.error();
+        return error;
     }
 
     (typedLayer->*setter)(*typedValue);
@@ -42,9 +43,10 @@ optional<Error> setPaintProperty(Layer& layer, const V& value, const optional<st
         return Error { "layer doesn't support this property" };
     }
 
-    Result<PropertyValue> typedValue = convert<PropertyValue>(value);
+    Error error;
+    optional<PropertyValue> typedValue = convert<PropertyValue>(value, error);
     if (!typedValue) {
-        return typedValue.error();
+        return error;
     }
 
     (typedLayer->*setter)(*typedValue, klass);
@@ -58,9 +60,10 @@ optional<Error> setTransition(Layer& layer, const V& value, const optional<std::
         return Error { "layer doesn't support this property" };
     }
 
-    Result<TransitionOptions> transition = convert<TransitionOptions>(value);
+    Error error;
+    optional<TransitionOptions> transition = convert<TransitionOptions>(value, error);
     if (!transition) {
-        return transition.error();
+        return error;
     }
 
     (typedLayer->*setter)(*transition, klass);
@@ -74,9 +77,10 @@ optional<Error> setVisibility(Layer& layer, const V& value) {
         return {};
     }
 
-    Result<VisibilityType> visibility = convert<VisibilityType>(value);
+    Error error;
+    optional<VisibilityType> visibility = convert<VisibilityType>(value, error);
     if (!visibility) {
-        return visibility.error();
+        return error;
     }
 
     layer.setVisibility(*visibility);
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index d5e2a5c3c8..f8937da07d 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -12,21 +12,21 @@ namespace conversion {
 template <class T>
 struct Converter<PropertyValue<T>> {
     template <class V>
-    Result<PropertyValue<T>> operator()(const V& value) const {
+    optional<PropertyValue<T>> operator()(const V& value, Error& error) const {
         if (isUndefined(value)) {
-            return {};
+            return PropertyValue<T>();
         } else if (isObject(value)) {
-            Result<CameraFunction<T>> function = convert<CameraFunction<T>>(value);
+            optional<CameraFunction<T>> function = convert<CameraFunction<T>>(value, error);
             if (!function) {
-                return function.error();
+                return {};
             }
-            return *function;
+            return { *function };
         } else {
-            Result<T> constant = convert<T>(value);
+            optional<T> constant = convert<T>(value, error);
             if (!constant) {
-                return constant.error();
+                return {};
             }
-            return *constant;
+            return { *constant };
         }
     }
 };
diff --git a/include/mbgl/style/conversion/source.hpp b/include/mbgl/style/conversion/source.hpp
index 6e1b4347c3..2371183b1c 100644
--- a/include/mbgl/style/conversion/source.hpp
+++ b/include/mbgl/style/conversion/source.hpp
@@ -17,59 +17,65 @@ template <>
 struct Converter<std::unique_ptr<Source>> {
 public:
     template <class V>
-    Result<std::unique_ptr<Source>> operator()(const V& value, const std::string& id) const {
+    optional<std::unique_ptr<Source>> operator()(const V& value, Error& error, const std::string& id) const {
         if (!isObject(value)) {
-            return Error{ "source must be an object" };
+            error = { "source must be an object" };
+            return {};
         }
 
         auto typeValue = objectMember(value, "type");
         if (!typeValue) {
-            return Error{ "source must have a type" };
+            error = { "source must have a type" };
+            return {};
         }
 
         optional<std::string> type = toString(*typeValue);
         if (!type) {
-            return Error{ "source type must be a string" };
+            error = { "source type must be a string" };
+            return {};
         }
 
         if (*type == "raster") {
-            return convertRasterSource(id, value);
+            return convertRasterSource(id, value, error);
         } else if (*type == "vector") {
-            return convertVectorSource(id, value);
+            return convertVectorSource(id, value, error);
         } else if (*type == "geojson") {
-            return convertGeoJSONSource(id, value);
+            return convertGeoJSONSource(id, value, error);
         } else {
-            return Error{ "invalid source type" };
+            error = { "invalid source type" };
+            return {};
         }
     }
 
 private:
     // A tile source can either specify a URL to TileJSON, or inline TileJSON.
     template <class V>
-    Result<variant<std::string, Tileset>> convertURLOrTileset(const V& value) const {
+    optional<variant<std::string, Tileset>> convertURLOrTileset(const V& value, Error& error) const {
         auto urlVal = objectMember(value, "url");
         if (!urlVal) {
-            Result<Tileset> tileset = convert<Tileset>(value);
+            optional<Tileset> tileset = convert<Tileset>(value, error);
             if (!tileset) {
-                return tileset.error();
+                return {};
             }
-            return *tileset;
+            return { *tileset };
         }
 
         optional<std::string> url = toString(*urlVal);
         if (!url) {
-            return Error{ "source url must be a string" };
+            error = { "source url must be a string" };
+            return {};
         }
 
-        return *url;
+        return { *url };
     }
 
     template <class V>
-    Result<std::unique_ptr<Source>> convertRasterSource(const std::string& id,
-                                                        const V& value) const {
-        Result<variant<std::string, Tileset>> urlOrTileset = convertURLOrTileset(value);
+    optional<std::unique_ptr<Source>> convertRasterSource(const std::string& id,
+                                                          const V& value,
+                                                          Error& error) const {
+        optional<variant<std::string, Tileset>> urlOrTileset = convertURLOrTileset(value, error);
         if (!urlOrTileset) {
-            return urlOrTileset.error();
+            return {};
         }
 
         uint16_t tileSize = util::tileSize;
@@ -77,53 +83,58 @@ private:
         if (tileSizeValue) {
             optional<float> size = toNumber(*tileSizeValue);
             if (!size || *size < 0 || *size > std::numeric_limits<uint16_t>::max()) {
-                return Error{ "invalid tileSize" };
+                error = { "invalid tileSize" };
+                return {};
             }
             tileSize = *size;
         }
 
-        return std::make_unique<RasterSource>(id, std::move(*urlOrTileset), tileSize);
+        return { std::make_unique<RasterSource>(id, std::move(*urlOrTileset), tileSize) };
     }
 
     template <class V>
-    Result<std::unique_ptr<Source>> convertVectorSource(const std::string& id,
-                                                        const V& value) const {
-        Result<variant<std::string, Tileset>> urlOrTileset = convertURLOrTileset(value);
+    optional<std::unique_ptr<Source>> convertVectorSource(const std::string& id,
+                                                          const V& value,
+                                                          Error& error) const {
+        optional<variant<std::string, Tileset>> urlOrTileset = convertURLOrTileset(value, error);
         if (!urlOrTileset) {
-            return urlOrTileset.error();
+            return {};
         }
 
-        return std::make_unique<VectorSource>(id, std::move(*urlOrTileset));
+        return { std::make_unique<VectorSource>(id, std::move(*urlOrTileset)) };
     }
 
     template <class V>
-    Result<std::unique_ptr<Source>> convertGeoJSONSource(const std::string& id,
-                                                         const V& value) const {
+    optional<std::unique_ptr<Source>> convertGeoJSONSource(const std::string& id,
+                                                           const V& value,
+                                                           Error& error) const {
         auto dataValue = objectMember(value, "data");
         if (!dataValue) {
-            return Error{ "GeoJSON source must have a data value" };
+            error = { "GeoJSON source must have a data value" };
+            return {};
         }
 
-        Result<GeoJSONOptions> options = convert<GeoJSONOptions>(value);
+        optional<GeoJSONOptions> options = convert<GeoJSONOptions>(value, error);
         if (!options) {
-            return options.error();
+            return {};
         }
 
         auto result = std::make_unique<GeoJSONSource>(id, *options);
 
         if (isObject(*dataValue)) {
-            Result<GeoJSON> geoJSON = convertGeoJSON(*dataValue);
+            optional<GeoJSON> geoJSON = convertGeoJSON(*dataValue, error);
             if (!geoJSON) {
-                return geoJSON.error();
+                return {};
             }
             result->setGeoJSON(std::move(*geoJSON));
         } else if (toString(*dataValue)) {
             result->setURL(*toString(*dataValue));
         } else {
-            return Error{ "GeoJSON data must be a URL or an object" };
+            error = { "GeoJSON data must be a URL or an object" };
+            return {};
         }
 
-        return std::move(result);
+        return { std::move(result) };
     }
 };
 
diff --git a/include/mbgl/style/conversion/tileset.hpp b/include/mbgl/style/conversion/tileset.hpp
index 1955cc16cf..377170aa6a 100644
--- a/include/mbgl/style/conversion/tileset.hpp
+++ b/include/mbgl/style/conversion/tileset.hpp
@@ -11,22 +11,25 @@ template <>
 struct Converter<Tileset> {
 public:
     template <class V>
-    Result<Tileset> operator()(const V& value) const {
+    optional<Tileset> operator()(const V& value, Error& error) const {
         Tileset result;
 
         auto tiles = objectMember(value, "tiles");
         if (!tiles) {
-            return Error { "source must have tiles" };
+            error = { "source must have tiles" };
+            return {};
         }
 
         if (!isArray(*tiles)) {
-            return Error { "source tiles must be an array" };
+            error = { "source tiles must be an array" };
+            return {};
         }
 
         for (std::size_t i = 0; i < arrayLength(*tiles); i++) {
             optional<std::string> urlTemplate = toString(arrayMember(*tiles, i));
             if (!urlTemplate) {
-                return Error { "source tiles member must be a string" };
+                error = { "source tiles member must be a string" };
+                return {};
             }
             result.tiles.push_back(std::move(*urlTemplate));
         }
@@ -43,7 +46,8 @@ public:
         if (minzoomValue) {
             optional<float> minzoom = toNumber(*minzoomValue);
             if (!minzoom || *minzoom < 0 || *minzoom > std::numeric_limits<uint8_t>::max()) {
-                return Error { "invalid minzoom" };
+                error = { "invalid minzoom" };
+                return {};
             }
             result.zoomRange.min = *minzoom;
         }
@@ -52,7 +56,8 @@ public:
         if (maxzoomValue) {
             optional<float> maxzoom = toNumber(*maxzoomValue);
             if (!maxzoom || *maxzoom < 0 || *maxzoom > std::numeric_limits<uint8_t>::max()) {
-                return Error { "invalid maxzoom" };
+                error = { "invalid maxzoom" };
+                return {};
             }
             result.zoomRange.max = *maxzoom;
         }
@@ -61,7 +66,8 @@ public:
         if (attributionValue) {
             optional<std::string> attribution = toString(*attributionValue);
             if (!attribution) {
-                return Error { "source attribution must be a string" };
+                error = { "source attribution must be a string" };
+                return {};
             }
             result.attribution = std::move(*attribution);
         }
diff --git a/include/mbgl/style/conversion/transition_options.hpp b/include/mbgl/style/conversion/transition_options.hpp
index cdd65cfe9f..de8834d578 100644
--- a/include/mbgl/style/conversion/transition_options.hpp
+++ b/include/mbgl/style/conversion/transition_options.hpp
@@ -11,9 +11,10 @@ template <>
 struct Converter<TransitionOptions> {
 public:
     template <class V>
-    Result<TransitionOptions> operator()(const V& value) const {
+    optional<TransitionOptions> operator()(const V& value, Error& error) const {
         if (!isObject(value)) {
-            return Error { "transition must be an object" };
+            error = { "transition must be an object" };
+            return {};
         }
 
         TransitionOptions result;
@@ -22,7 +23,8 @@ public:
         if (duration) {
             auto number = toNumber(*duration);
             if (!number) {
-                return Error { "duration must be a number" };
+                error = { "duration must be a number" };
+                return {};
             }
             result.duration = { std::chrono::milliseconds(int64_t(*number)) };
         }
@@ -31,7 +33,8 @@ public:
         if (delay) {
             auto number = toNumber(*delay);
             if (!number) {
-                return Error { "delay must be a number" };
+                error = { "delay must be a number" };
+                return {};
             }
             result.delay = { std::chrono::milliseconds(int64_t(*number)) };
         }
diff --git a/platform/android/src/style/conversion/filter.hpp b/platform/android/src/style/conversion/filter.hpp
index fc36d3a044..1f0abcf3a4 100644
--- a/platform/android/src/style/conversion/filter.hpp
+++ b/platform/android/src/style/conversion/filter.hpp
@@ -17,9 +17,10 @@ inline optional<mbgl::style::Filter> toFilter(jni::JNIEnv& env, jni::Array<jni::
     mbgl::optional<mbgl::style::Filter> filter;
     if (jfilter) {
       Value filterValue(env, jfilter);
-      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(filterValue);
+      mbgl::style::conversion::Error error;
+      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(filterValue, error);
       if (!converted) {
-          mbgl::Log::Error(mbgl::Event::JNI, "Error converting filter: " + converted.error().message);
+          mbgl::Log::Error(mbgl::Event::JNI, "Error converting filter: " + error.message);
       }
       filter = std::move(*converted);
     }
diff --git a/platform/android/src/style/conversion/geojson.hpp b/platform/android/src/style/conversion/geojson.hpp
index 415d96f467..6ac6abcd7c 100644
--- a/platform/android/src/style/conversion/geojson.hpp
+++ b/platform/android/src/style/conversion/geojson.hpp
@@ -17,12 +17,13 @@ namespace style {
 namespace conversion {
 
 template <>
-Result<GeoJSON> convertGeoJSON(const mbgl::android::Value& value) {
+optional<GeoJSON> convertGeoJSON(const mbgl::android::Value& value, Error& error) {
 
     // Value should be a string wrapped in an object
     mbgl::android::Value jsonValue = value.get("data");
     if(value.isNull()) {
-        return Error { "no json data found" };
+        error = { "no json data found" };
+        return {};
     }
     std::string jsonString = value.get("data").toString();
 
@@ -32,12 +33,14 @@ Result<GeoJSON> convertGeoJSON(const mbgl::android::Value& value) {
     if (d.HasParseError()) {
         std::stringstream message;
         message << d.GetErrorOffset() << " - " << rapidjson::GetParseError_En(d.GetParseError());
-        return Error { message.str() };
+        error = { message.str() };
+        return {};
     }
 
-    conversion::Result<GeoJSON> geoJSON = conversion::convertGeoJSON<JSValue>(d);
+    optional<GeoJSON> geoJSON = conversion::convertGeoJSON<JSValue>(d, error);
     if (!geoJSON) {
-        return Error { geoJSON.error().message };
+        error = { error.message };
+        return {};
     }
 
     return geoJSON;
@@ -46,8 +49,8 @@ Result<GeoJSON> convertGeoJSON(const mbgl::android::Value& value) {
 template <>
 struct Converter<GeoJSON> {
 
-    Result<GeoJSON> operator()(const mbgl::android::Value& value) const {
-        return convertGeoJSON(value);
+    optional<GeoJSON> operator()(const mbgl::android::Value& value, Error& error) const {
+        return convertGeoJSON(value, error);
     }
 
 };
diff --git a/platform/android/src/style/conversion/url_or_tileset.hpp b/platform/android/src/style/conversion/url_or_tileset.hpp
index 4e502324d0..00ef913d41 100644
--- a/platform/android/src/style/conversion/url_or_tileset.hpp
+++ b/platform/android/src/style/conversion/url_or_tileset.hpp
@@ -12,27 +12,25 @@
 #include <string>
 
 namespace mbgl {
-namespace style {
-namespace conversion {
-
-template <>
-struct Converter<variant<std::string, Tileset>> {
-
-    template <class V>
-    Result<variant<std::string, Tileset>> operator()(const V& value) const {
-        if (isObject(value)) {
-            Result<Tileset> tileset = convert<Tileset>(value);
-            if (!tileset) {
-                return tileset.error();
-            }
-            return *tileset;
-        } else {
-            return *toString(value);
+namespace android {
+
+// This conversion is expected not to fail because it's used only in contexts where
+// the value was originally a String or TileSet object on the Java side. If it fails
+// to convert, it's a bug in our serialization or Java-side static typing.
+inline variant<std::string, Tileset> convertURLOrTileset(const Value& value) {
+    using namespace mbgl::style::conversion;
+
+    if (isObject(value)) {
+        Error error;
+        optional<Tileset> tileset = convert<Tileset>(value, error);
+        if (!tileset) {
+            throw std::logic_error(error.message);
         }
+        return { *tileset };
+    } else {
+        return { *toString(value) };
     }
-
-};
-
 }
+
 }
 }
diff --git a/platform/android/src/style/layers/layer.cpp b/platform/android/src/style/layers/layer.cpp
index dbf71fd2af..6e93cf4daf 100644
--- a/platform/android/src/style/layers/layer.cpp
+++ b/platform/android/src/style/layers/layer.cpp
@@ -104,9 +104,10 @@ namespace android {
         Value wrapped(env, jfilter);
         Filter filter;
 
-        Result<Filter> converted = convert<Filter>(wrapped);
+        Error error;
+        optional<Filter> converted = convert<Filter>(wrapped, error);
         if (!converted) {
-            mbgl::Log::Error(mbgl::Event::JNI, "Error setting filter: " + converted.error().message);
+            mbgl::Log::Error(mbgl::Event::JNI, "Error setting filter: " + error.message);
             return;
         }
         filter = std::move(*converted);
diff --git a/platform/android/src/style/sources/geojson_source.cpp b/platform/android/src/style/sources/geojson_source.cpp
index 7ab98e47c0..0c2d25f9fc 100644
--- a/platform/android/src/style/sources/geojson_source.cpp
+++ b/platform/android/src/style/sources/geojson_source.cpp
@@ -9,7 +9,7 @@
 #include "../../conversion/conversion.hpp"
 #include "../../conversion/collection.hpp"
 #include "../../geometry/conversion/feature.hpp"
-#include "../conversion/url_or_tileset.hpp"
+
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/geojson_options.hpp>
 
@@ -18,11 +18,26 @@
 namespace mbgl {
 namespace android {
 
+    // This conversion is expected not to fail because it's used only in contexts where
+    // the value was originally a GeoJsonOptions object on the Java side. If it fails
+    // to convert, it's a bug in our serialization or Java-side static typing.
+    static style::GeoJSONOptions convertGeoJSONOptions(jni::JNIEnv& env, jni::Object<> options) {
+        using namespace mbgl::style::conversion;
+        if (!options) {
+            return style::GeoJSONOptions();
+        }
+        Error error;
+        optional<style::GeoJSONOptions> result = convert<style::GeoJSONOptions>(Value(env, options), error);
+        if (!result) {
+            throw std::logic_error(error.message);
+        }
+        return *result;
+    }
+
     GeoJSONSource::GeoJSONSource(jni::JNIEnv& env, jni::String sourceId, jni::Object<> options)
         : Source(env, std::make_unique<mbgl::style::GeoJSONSource>(
                 jni::Make<std::string>(env, sourceId),
-                options ? *style::conversion::convert<style::GeoJSONOptions>(Value(env, options)) : style::GeoJSONOptions()
-                )
+                convertGeoJSONOptions(env, options))
             ) {
     }
 
@@ -36,9 +51,10 @@ namespace android {
         using namespace mbgl::style::conversion;
 
         // Convert the jni object
-        Result<GeoJSON> converted = convert<GeoJSON>(Value(env, json));
+        Error error;
+        optional<GeoJSON> converted = convert<GeoJSON>(Value(env, json), error);
         if(!converted) {
-            mbgl::Log::Error(mbgl::Event::JNI, "Error setting geo json: " + converted.error().message);
+            mbgl::Log::Error(mbgl::Event::JNI, "Error setting geo json: " + error.message);
             return;
         }
 
diff --git a/platform/android/src/style/sources/raster_source.cpp b/platform/android/src/style/sources/raster_source.cpp
index 42ac4cda99..0234901a77 100644
--- a/platform/android/src/style/sources/raster_source.cpp
+++ b/platform/android/src/style/sources/raster_source.cpp
@@ -16,7 +16,7 @@ namespace android {
             env,
             std::make_unique<mbgl::style::RasterSource>(
                 jni::Make<std::string>(env, sourceId),
-                *style::conversion::convert<variant<std::string, Tileset>>(Value(env, urlOrTileSet)),
+                convertURLOrTileset(Value(env, urlOrTileSet)),
                 tileSize
             )
         ) {
diff --git a/platform/android/src/style/sources/vector_source.cpp b/platform/android/src/style/sources/vector_source.cpp
index 67777f50d4..4852a9b84f 100644
--- a/platform/android/src/style/sources/vector_source.cpp
+++ b/platform/android/src/style/sources/vector_source.cpp
@@ -23,7 +23,7 @@ namespace android {
             env,
             std::make_unique<mbgl::style::VectorSource>(
                 jni::Make<std::string>(env, sourceId),
-                *style::conversion::convert<variant<std::string, Tileset>>(Value(env, urlOrTileSet))
+                convertURLOrTileset(Value(env, urlOrTileSet))
             )
         ) {
     }
diff --git a/platform/darwin/src/MGLStyleValue_Private.h b/platform/darwin/src/MGLStyleValue_Private.h
index 90d6622c93..263b54d7e5 100644
--- a/platform/darwin/src/MGLStyleValue_Private.h
+++ b/platform/darwin/src/MGLStyleValue_Private.h
@@ -123,8 +123,9 @@ public:
             return toMBGLConstantValue((MGLConstantStyleValue<ObjCType> *)value);
         } else if ([value isKindOfClass:[MGLStyleFunction class]]) {
             auto rawValue = toRawStyleSpecValue((MGLStyleFunction<ObjCType> *) value);
-            auto result = mbgl::style::conversion::convert<mbgl::style::DataDrivenPropertyValue<MBGLType>>(rawValue);
-            NSCAssert(result, @(result.error().message.c_str()));
+            mbgl::style::conversion::Error error;
+            auto result = mbgl::style::conversion::convert<mbgl::style::DataDrivenPropertyValue<MBGLType>>(rawValue, error);
+            NSCAssert(result, @(error.message.c_str()));
             return *result;
         } else {
             return {};
diff --git a/platform/node/src/node_geojson.hpp b/platform/node/src/node_geojson.hpp
index ace4c91426..e4b2ca47e7 100644
--- a/platform/node/src/node_geojson.hpp
+++ b/platform/node/src/node_geojson.hpp
@@ -5,8 +5,9 @@ namespace style {
 namespace conversion {
 
 template <>
-Result<GeoJSON> convertGeoJSON(const v8::Local<v8::Value>&) {
-    return Error { "not implemented" };
+optional<GeoJSON> convertGeoJSON(const v8::Local<v8::Value>&, Error& error) {
+    error = { "not implemented" };
+    return {};
 }
 
 } // namespace conversion
diff --git a/platform/node/src/node_map.cpp b/platform/node/src/node_map.cpp
index a3a11a1907..881c1b2fb7 100644
--- a/platform/node/src/node_map.cpp
+++ b/platform/node/src/node_map.cpp
@@ -538,9 +538,10 @@ void NodeMap::AddSource(const Nan::FunctionCallbackInfo<v8::Value>& info) {
         return Nan::ThrowTypeError("First argument must be a string");
     }
 
-    Result<std::unique_ptr<Source>> source = convert<std::unique_ptr<Source>>(info[1], *Nan::Utf8String(info[0]));
+    Error error;
+    mbgl::optional<std::unique_ptr<Source>> source = convert<std::unique_ptr<Source>>(info[1], error, *Nan::Utf8String(info[0]));
     if (!source) {
-        Nan::ThrowTypeError(source.error().message.c_str());
+        Nan::ThrowTypeError(error.message.c_str());
         return;
     }
 
@@ -558,9 +559,10 @@ void NodeMap::AddLayer(const Nan::FunctionCallbackInfo<v8::Value>& info) {
         return Nan::ThrowTypeError("One argument required");
     }
 
-    Result<std::unique_ptr<Layer>> layer = convert<std::unique_ptr<Layer>>(info[0]);
+    Error error;
+    mbgl::optional<std::unique_ptr<Layer>> layer = convert<std::unique_ptr<Layer>>(info[0], error);
     if (!layer) {
-        Nan::ThrowTypeError(layer.error().message.c_str());
+        Nan::ThrowTypeError(error.message.c_str());
         return;
     }
 
@@ -774,9 +776,10 @@ void NodeMap::SetFilter(const Nan::FunctionCallbackInfo<v8::Value>& info) {
     Filter filter;
 
     if (!info[1]->IsNull() && !info[1]->IsUndefined()) {
-        Result<Filter> converted = convert<Filter>(info[1]);
+        Error error;
+        mbgl::optional<Filter> converted = convert<Filter>(info[1], error);
         if (!converted) {
-            Nan::ThrowTypeError(converted.error().message.c_str());
+            Nan::ThrowTypeError(error.message.c_str());
             return;
         }
         filter = std::move(*converted);
@@ -908,23 +911,24 @@ void NodeMap::QueryRenderedFeatures(const Nan::FunctionCallbackInfo<v8::Value>&
         //Check if filter is provided. If set it must be a valid Filter object
         if (Nan::Has(options, Nan::New("filter").ToLocalChecked()).FromJust()) {
             auto filterOption = Nan::Get(options, Nan::New("filter").ToLocalChecked()).ToLocalChecked();
-            Result<Filter> converted = convert<Filter>(filterOption);
+            Error error;
+            mbgl::optional<Filter> converted = convert<Filter>(filterOption, error);
             if (!converted) {
-                return Nan::ThrowTypeError(converted.error().message.c_str());
+                return Nan::ThrowTypeError(error.message.c_str());
             }
             queryOptions.filter = std::move(*converted);
         }
     }
 
     try {
-        std::vector<mbgl::Feature> result;
+        std::vector<mbgl::Feature> optional;
 
         if (Nan::Get(posOrBox, 0).ToLocalChecked()->IsArray()) {
 
             auto pos0 = Nan::Get(posOrBox, 0).ToLocalChecked().As<v8::Array>();
             auto pos1 = Nan::Get(posOrBox, 1).ToLocalChecked().As<v8::Array>();
 
-            result = nodeMap->map->queryRenderedFeatures(mbgl::ScreenBox {
+            optional = nodeMap->map->queryRenderedFeatures(mbgl::ScreenBox {
                 {
                     Nan::Get(pos0, 0).ToLocalChecked()->NumberValue(),
                     Nan::Get(pos0, 1).ToLocalChecked()->NumberValue()
@@ -935,15 +939,15 @@ void NodeMap::QueryRenderedFeatures(const Nan::FunctionCallbackInfo<v8::Value>&
             },  queryOptions);
 
         } else {
-            result = nodeMap->map->queryRenderedFeatures(mbgl::ScreenCoordinate {
+            optional = nodeMap->map->queryRenderedFeatures(mbgl::ScreenCoordinate {
                 Nan::Get(posOrBox, 0).ToLocalChecked()->NumberValue(),
                 Nan::Get(posOrBox, 1).ToLocalChecked()->NumberValue()
             }, queryOptions);
         }
 
         auto array = Nan::New<v8::Array>();
-        for (unsigned int i = 0; i < result.size(); i++) {
-            array->Set(i, toJS(result[i]));
+        for (unsigned int i = 0; i < optional.size(); i++) {
+            array->Set(i, toJS(optional[i]));
         }
         info.GetReturnValue().Set(array);
     } catch (const std::exception &ex) {
diff --git a/platform/qt/src/qmapboxgl.cpp b/platform/qt/src/qmapboxgl.cpp
index b1c0a11ee1..3d5da10c36 100644
--- a/platform/qt/src/qmapboxgl.cpp
+++ b/platform/qt/src/qmapboxgl.cpp
@@ -1250,9 +1250,10 @@ void QMapboxGL::addSource(const QString &id, const QVariantMap &params)
     using namespace mbgl::style;
     using namespace mbgl::style::conversion;
 
-    Result<std::unique_ptr<Source>> source = convert<std::unique_ptr<Source>>(QVariant(params), id.toStdString());
+    Error error;
+    mbgl::optional<std::unique_ptr<Source>> source = convert<std::unique_ptr<Source>>(QVariant(params), error, id.toStdString());
     if (!source) {
-        qWarning() << "Unable to add source:" << source.error().message.c_str();
+        qWarning() << "Unable to add source:" << error.message.c_str();
         return;
     }
 
@@ -1291,7 +1292,8 @@ void QMapboxGL::updateSource(const QString &id, const QVariantMap &params)
     }
 
     if (params.contains("data")) {
-        auto result = convertGeoJSON(params["data"]);
+        Error error;
+        auto result = convertGeoJSON(params["data"], error);
         if (result) {
             sourceGeoJSON->setGeoJSON(*result);
         }
@@ -1362,9 +1364,10 @@ void QMapboxGL::addLayer(const QVariantMap &params)
     using namespace mbgl::style;
     using namespace mbgl::style::conversion;
 
-    Result<std::unique_ptr<Layer>> layer = convert<std::unique_ptr<Layer>>(QVariant(params));
+    Error error;
+    mbgl::optional<std::unique_ptr<Layer>> layer = convert<std::unique_ptr<Layer>>(QVariant(params), error);
     if (!layer) {
-        qWarning() << "Unable to add layer:" << layer.error().message.c_str();
+        qWarning() << "Unable to add layer:" << error.message.c_str();
         return;
     }
 
@@ -1445,9 +1448,10 @@ void QMapboxGL::setFilter(const QString& layer, const QVariant& filter)
 
     Filter filter_;
 
-    Result<Filter> converted = convert<Filter>(filter);
+    Error error;
+    mbgl::optional<Filter> converted = convert<Filter>(filter, error);
     if (!converted) {
-        qWarning() << "Error parsing filter:" << converted.error().message.c_str();
+        qWarning() << "Error parsing filter:" << error.message.c_str();
         return;
     }
     filter_ = std::move(*converted);
diff --git a/platform/qt/src/qt_geojson.hpp b/platform/qt/src/qt_geojson.hpp
index 038b051941..7c50c663dd 100644
--- a/platform/qt/src/qt_geojson.hpp
+++ b/platform/qt/src/qt_geojson.hpp
@@ -180,20 +180,21 @@ namespace style {
 namespace conversion {
 
 template <>
-Result<GeoJSON> convertGeoJSON(const QMapbox::Feature& feature) {
-    return Result<GeoJSON> { GeoJSON { asMapboxGLFeature(feature) } };
+optional<GeoJSON> convertGeoJSON(const QMapbox::Feature& feature, Error&) {
+    return GeoJSON { asMapboxGLFeature(feature) };
 }
 
 template <>
-Result<GeoJSON> convertGeoJSON(const QVariant& value) {
+optional<GeoJSON> convertGeoJSON(const QVariant& value, Error& error) {
 #if QT_VERSION >= 0x050000
     if (value.typeName() == QStringLiteral("QMapbox::Feature")) {
 #else
     if (value.typeName() == QString("QMapbox::Feature")) {
 #endif
-        return convertGeoJSON(value.value<QMapbox::Feature>());
+        return convertGeoJSON(value.value<QMapbox::Feature>(), error);
     } else if (value.type() != QVariant::ByteArray) {
-        return Error { "JSON data must be in QByteArray" };
+        error = { "JSON data must be in QByteArray" };
+        return {};
     }
 
     auto data = value.toByteArray();
@@ -208,13 +209,14 @@ Result<GeoJSON> convertGeoJSON(const QVariant& value) {
     if (d.HasParseError()) {
         std::stringstream message;
         message << d.GetErrorOffset() << " - " << rapidjson::GetParseError_En(d.GetParseError());
-
-        return Error { message.str() };
+        error = { message.str() };
+        return {};
     }
 
-    Result<GeoJSON> geoJSON = convertGeoJSON<JSValue>(d);
+    optional<GeoJSON> geoJSON = convertGeoJSON<JSValue>(d, error);
     if (!geoJSON) {
-        return Error { geoJSON.error().message };
+        error = { error.message };
+        return {};
     }
 
     return geoJSON;
diff --git a/src/mbgl/style/parser.cpp b/src/mbgl/style/parser.cpp
index 926c243733..d970d8bbc0 100644
--- a/src/mbgl/style/parser.cpp
+++ b/src/mbgl/style/parser.cpp
@@ -116,10 +116,11 @@ void Parser::parseSources(const JSValue& value) {
     for (const auto& property : value.GetObject()) {
         std::string id = *conversion::toString(property.name);
 
-        conversion::Result<std::unique_ptr<Source>> source =
-            conversion::convert<std::unique_ptr<Source>>(property.value, id);
+        conversion::Error error;
+        optional<std::unique_ptr<Source>> source =
+            conversion::convert<std::unique_ptr<Source>>(property.value, error, id);
         if (!source) {
-            Log::Warning(Event::ParseStyle, source.error().message);
+            Log::Warning(Event::ParseStyle, error.message);
             continue;
         }
 
@@ -222,9 +223,10 @@ void Parser::parseLayer(const std::string& id, const JSValue& value, std::unique
         layer = reference->baseImpl->cloneRef(id);
         conversion::setPaintProperties(*layer, value);
     } else {
-        conversion::Result<std::unique_ptr<Layer>> converted = conversion::convert<std::unique_ptr<Layer>>(value);
+        conversion::Error error;
+        optional<std::unique_ptr<Layer>> converted = conversion::convert<std::unique_ptr<Layer>>(value, error);
         if (!converted) {
-            Log::Warning(Event::ParseStyle, converted.error().message);
+            Log::Warning(Event::ParseStyle, error.message);
             return;
         }
         layer = std::move(*converted);
@@ -232,20 +234,20 @@ void Parser::parseLayer(const std::string& id, const JSValue& value, std::unique
 }
 
 std::vector<FontStack> Parser::fontStacks() const {
-    std::set<FontStack> result;
+    std::set<FontStack> optional;
 
     for (const auto& layer : layers) {
         if (layer->is<SymbolLayer>()) {
             PropertyValue<FontStack> textFont = layer->as<SymbolLayer>()->getTextFont();
             if (textFont.isUndefined()) {
-                result.insert({"Open Sans Regular", "Arial Unicode MS Regular"});
+                optional.insert({"Open Sans Regular", "Arial Unicode MS Regular"});
             } else if (textFont.isConstant()) {
-                result.insert(textFont.asConstant());
+                optional.insert(textFont.asConstant());
             } else if (textFont.isCameraFunction()) {
                 textFont.asCameraFunction().stops.match(
                     [&] (const auto& stops) {
                         for (const auto& stop : stops.stops) {
-                            result.insert(stop.second);
+                            optional.insert(stop.second);
                         }
                     }
                 );
@@ -253,7 +255,7 @@ std::vector<FontStack> Parser::fontStacks() const {
         }
     }
 
-    return std::vector<FontStack>(result.begin(), result.end());
+    return std::vector<FontStack>(optional.begin(), optional.end());
 }
 
 } // namespace style
diff --git a/src/mbgl/style/property_parsing.cpp b/src/mbgl/style/property_parsing.cpp
deleted file mode 100644
index 16ce0f4adc..0000000000
--- a/src/mbgl/style/property_parsing.cpp
+++ /dev/null
@@ -1,29 +0,0 @@
-#include <mbgl/style/property_parsing.hpp>
-
-namespace mbgl {
-namespace style {
-
-optional<TransitionOptions> parseTransitionOptions(const char *, const JSValue& value) {
-    if (!value.IsObject()) {
-        return {};
-    }
-
-    optional<Duration> duration;
-    if (value.HasMember("duration") && value["duration"].IsNumber()) {
-        duration.emplace(Milliseconds(value["duration"].GetUint()));
-    }
-
-    optional<Duration> delay;
-    if (value.HasMember("delay") && value["delay"].IsNumber()) {
-        delay.emplace(Milliseconds(value["delay"].GetUint()));
-    }
-
-    if (!duration && !delay) {
-        return {};
-    }
-
-    return TransitionOptions { duration, delay };
-}
-
-} // namespace style
-} // namespace mbgl
diff --git a/src/mbgl/style/property_parsing.hpp b/src/mbgl/style/property_parsing.hpp
deleted file mode 100644
index b542c8ae47..0000000000
--- a/src/mbgl/style/property_parsing.hpp
+++ /dev/null
@@ -1,26 +0,0 @@
-#pragma once
-
-#include <mbgl/style/property_value.hpp>
-#include <mbgl/style/transition_options.hpp>
-#include <mbgl/style/rapidjson_conversion.hpp>
-#include <mbgl/style/conversion/property_value.hpp>
-
-#include <mbgl/util/logging.hpp>
-
-namespace mbgl {
-namespace style {
-
-template <typename T>
-PropertyValue<T> parseProperty(const char* name, const JSValue& value) {
-    conversion::Result<PropertyValue<T>> result = conversion::convert<PropertyValue<T>>(value);
-    if (!result) {
-        Log::Warning(Event::ParseStyle, "%s: %s", name, result.error().message);
-        return {};
-    }
-    return *result;
-}
-
-optional<TransitionOptions> parseTransitionOptions(const char * name, const JSValue&);
-
-} // namespace style
-} // namespace mbgl
diff --git a/src/mbgl/style/sources/geojson_source_impl.cpp b/src/mbgl/style/sources/geojson_source_impl.cpp
index b050e5482e..6431d5faa4 100644
--- a/src/mbgl/style/sources/geojson_source_impl.cpp
+++ b/src/mbgl/style/sources/geojson_source_impl.cpp
@@ -21,11 +21,12 @@ namespace style {
 namespace conversion {
 
 template <>
-Result<GeoJSON> convertGeoJSON(const JSValue& value) {
+optional<GeoJSON> convertGeoJSON(const JSValue& value, Error& error) {
     try {
         return mapbox::geojson::convert(value);
     } catch (const std::exception& ex) {
-        return Error{ ex.what() };
+        error = { ex.what() };
+        return {};
     }
 }
 } // namespace conversion
@@ -136,10 +137,11 @@ void GeoJSONSource::Impl::loadDescription(FileSource& fileSource) {
 
             invalidateTiles();
 
-            conversion::Result<GeoJSON> geoJSON = conversion::convertGeoJSON<JSValue>(d);
+            conversion::Error error;
+            optional<GeoJSON> geoJSON = conversion::convertGeoJSON<JSValue>(d, error);
             if (!geoJSON) {
                 Log::Error(Event::ParseStyle, "Failed to parse GeoJSON data: %s",
-                           geoJSON.error().message.c_str());
+                           error.message.c_str());
                 // Create an empty GeoJSON VT object to make sure we're not infinitely waiting for
                 // tiles to load.
                 _setGeoJSON(GeoJSON{ FeatureCollection{} });
diff --git a/src/mbgl/style/tile_source_impl.cpp b/src/mbgl/style/tile_source_impl.cpp
index daa6389a8e..9ea596d38b 100644
--- a/src/mbgl/style/tile_source_impl.cpp
+++ b/src/mbgl/style/tile_source_impl.cpp
@@ -24,9 +24,10 @@ Tileset TileSourceImpl::parseTileJSON(const std::string& json, const std::string
         throw std::runtime_error(message.str());
     }
 
-    conversion::Result<Tileset> result = conversion::convert<Tileset, JSValue>(document);
+    conversion::Error error;
+    optional<Tileset> result = conversion::convert<Tileset, JSValue>(document, error);
     if (!result) {
-        throw std::runtime_error(result.error().message);
+        throw std::runtime_error(error.message);
     }
 
     // TODO: Remove this hack by delivering proper URLs in the TileJSON to begin with.
diff --git a/test/style/conversion/function.test.cpp b/test/style/conversion/function.test.cpp
index 4dc6549c78..08637d40cb 100644
--- a/test/style/conversion/function.test.cpp
+++ b/test/style/conversion/function.test.cpp
@@ -10,45 +10,47 @@ using namespace mbgl;
 using namespace mbgl::style;
 using namespace mbgl::style::conversion;
 
-auto parseFunction(const std::string& src) {
-    JSDocument doc;
-    doc.Parse<0>(src);
-    return convert<CameraFunction<float>, JSValue>(doc);
-}
-
 TEST(StyleConversion, Function) {
+    Error error;
+
+    auto parseFunction = [&](const std::string& src) {
+        JSDocument doc;
+        doc.Parse<0>(src);
+        return convert<CameraFunction<float>, JSValue>(doc, error);
+    };
+
     auto fn1 = parseFunction("{\"stops\":[]}");
     ASSERT_FALSE(fn1);
-    ASSERT_EQ("function must have at least one stop", fn1.error().message);
+    ASSERT_EQ("function must have at least one stop", error.message);
 
     auto fn2 = parseFunction("{\"stops\":[1]}");
     ASSERT_FALSE(fn2);
-    ASSERT_EQ("function stop must be an array", fn2.error().message);
+    ASSERT_EQ("function stop must be an array", error.message);
 
     auto fn3 = parseFunction("{\"stops\":[[]]}");
     ASSERT_FALSE(fn3);
-    ASSERT_EQ("function stop must have two elements", fn3.error().message);
+    ASSERT_EQ("function stop must have two elements", error.message);
 
     auto fn4 = parseFunction("{\"stops\":[[-1,-1]]}");
     ASSERT_TRUE(bool(fn4));
 
     auto fn5 = parseFunction("{\"stops\":[[0,1,2]]}");
     ASSERT_FALSE(fn5);
-    ASSERT_EQ("function stop must have two elements", fn5.error().message);
+    ASSERT_EQ("function stop must have two elements", error.message);
 
     auto fn6 = parseFunction("{\"stops\":[[0,\"x\"]]}");
     ASSERT_FALSE(fn6);
-    ASSERT_EQ("value must be a number", fn6.error().message);
+    ASSERT_EQ("value must be a number", error.message);
 
     auto fn7 = parseFunction("{}");
     ASSERT_FALSE(fn7);
-    ASSERT_EQ("function value must specify stops", fn7.error().message);
+    ASSERT_EQ("function value must specify stops", error.message);
 
     auto fn8 = parseFunction("[]");
     ASSERT_FALSE(fn8);
-    ASSERT_EQ("function must be an object", fn8.error().message);
+    ASSERT_EQ("function must be an object", error.message);
 
     auto fn9 = parseFunction("{\"stops\":[[0,0]],\"base\":false}");
     ASSERT_FALSE(fn9);
-    ASSERT_EQ("function base must be a number", fn9.error().message);
+    ASSERT_EQ("function base must be a number", error.message);
 }
diff --git a/test/style/conversion/geojson_options.test.cpp b/test/style/conversion/geojson_options.test.cpp
index ddf261ea52..e6bd984f36 100644
--- a/test/style/conversion/geojson_options.test.cpp
+++ b/test/style/conversion/geojson_options.test.cpp
@@ -12,21 +12,24 @@ using namespace mbgl::style::conversion;
 TEST(GeoJSONOptions, Basic) {
     ValueMap map;
     Value raw(map);
-    Result<GeoJSONOptions> converted = convert<GeoJSONOptions>(raw);
+    Error error;
+    mbgl::optional<GeoJSONOptions> converted = convert<GeoJSONOptions>(raw, error);
     ASSERT_TRUE((bool) converted);
 }
 
 TEST(GeoJSONOptions, ErrorHandling) {
     ValueMap map {{"maxzoom", std::string{"should not be a string"}}};
     Value raw(map);
-    Result<GeoJSONOptions> converted = convert<GeoJSONOptions>(raw);
+    Error error;
+    mbgl::optional<GeoJSONOptions> converted = convert<GeoJSONOptions>(raw, error);
     ASSERT_FALSE((bool) converted);
 }
 
 TEST(GeoJSONOptions, RetainsDefaults) {
     ValueMap map;
     Value raw(map);
-    GeoJSONOptions converted = *convert<GeoJSONOptions>(raw);
+    Error error;
+    GeoJSONOptions converted = *convert<GeoJSONOptions>(raw, error);
     GeoJSONOptions defaults;
 
     // GeoJSON-VT
@@ -54,7 +57,8 @@ TEST(GeoJSONOptions, FullConversion) {
         {"clusterMaxZoom", 5.0f}
     };
     Value raw(map);
-    GeoJSONOptions converted = *convert<GeoJSONOptions>(raw);
+    Error error;
+    GeoJSONOptions converted = *convert<GeoJSONOptions>(raw, error);
 
     // GeoJSON-VT
     ASSERT_EQ(converted.maxzoom, 1);
diff --git a/test/style/conversion/layer.test.cpp b/test/style/conversion/layer.test.cpp
index b27c1841ee..cfe2662fb8 100644
--- a/test/style/conversion/layer.test.cpp
+++ b/test/style/conversion/layer.test.cpp
@@ -11,10 +11,11 @@ using namespace mbgl::style;
 using namespace mbgl::style::conversion;
 using namespace std::literals::chrono_literals;
 
-auto parseLayer(const std::string& src) {
+std::unique_ptr<Layer> parseLayer(const std::string& src) {
     JSDocument doc;
     doc.Parse<0>(src);
-    return convert<std::unique_ptr<Layer>, JSValue>(doc);
+    Error error;
+    return std::move(*convert<std::unique_ptr<Layer>, JSValue>(doc, error));
 }
 
 TEST(StyleConversion, LayerTransition) {
@@ -34,13 +35,13 @@ TEST(StyleConversion, LayerTransition) {
         }
     })JSON");
 
-    ASSERT_EQ(400ms, *(*layer)->as<BackgroundLayer>()->impl->paint.cascading
+    ASSERT_EQ(400ms, *layer->as<BackgroundLayer>()->impl->paint.cascading
         .get<BackgroundColor>().getTransition({}).duration);
-    ASSERT_EQ(500ms, *(*layer)->as<BackgroundLayer>()->impl->paint.cascading
+    ASSERT_EQ(500ms, *layer->as<BackgroundLayer>()->impl->paint.cascading
         .get<BackgroundColor>().getTransition({}).delay);
 
-    ASSERT_EQ(100ms, *(*layer)->as<BackgroundLayer>()->impl->paint.cascading
+    ASSERT_EQ(100ms, *layer->as<BackgroundLayer>()->impl->paint.cascading
         .get<BackgroundColor>().getTransition({"class"}).duration);
-    ASSERT_FALSE(bool((*layer)->as<BackgroundLayer>()->impl->paint.cascading
+    ASSERT_FALSE(bool(layer->as<BackgroundLayer>()->impl->paint.cascading
         .get<BackgroundColor>().getTransition({"class"}).delay));
 }
diff --git a/test/style/filter.test.cpp b/test/style/filter.test.cpp
index 2f12246078..c70792d8ef 100644
--- a/test/style/filter.test.cpp
+++ b/test/style/filter.test.cpp
@@ -16,7 +16,10 @@ using namespace mbgl::style;
 Filter parse(const char * expression) {
     rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> doc;
     doc.Parse<0>(expression);
-    return *conversion::convert<Filter, JSValue>(doc);
+    conversion::Error error;
+    optional<Filter> filter = conversion::convert<Filter, JSValue>(doc, error);
+    EXPECT_TRUE(bool(filter));
+    return *filter;
 }
 
 Feature feature(const PropertyMap& properties, const Geometry<double>& geometry = Point<double>()) {