Replace compile-time polymorphism with runtime polymorphism in the conversion system

19 files changed, 644 insertions, 586 deletions

diff --git a/platform/android/config.cmake b/platform/android/config.cmake
index 8dd537d36e..db75b850f1 100644
--- a/platform/android/config.cmake
+++ b/platform/android/config.cmake
@@ -146,7 +146,6 @@ add_library(mbgl-android STATIC
 
     # Style conversion Java -> C++
     platform/android/src/style/android_conversion.hpp
-    platform/android/src/style/conversion/geojson.hpp
     platform/android/src/style/value.cpp
     platform/android/src/style/value.hpp
     platform/android/src/style/conversion/url_or_tileset.hpp
diff --git a/platform/android/src/style/android_conversion.hpp b/platform/android/src/style/android_conversion.hpp
index 082fe411e2..510a9f8444 100644
--- a/platform/android/src/style/android_conversion.hpp
+++ b/platform/android/src/style/android_conversion.hpp
@@ -4,8 +4,9 @@
 
 #include <mbgl/util/feature.hpp>
 #include <mbgl/util/logging.hpp>
-#include <mbgl/style/conversion.hpp>
 #include <mbgl/util/optional.hpp>
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
 
 #include <jni/jni.hpp>
 
@@ -13,89 +14,105 @@ namespace mbgl {
 namespace style {
 namespace conversion {
 
-inline bool isUndefined(const mbgl::android::Value& value) {
-    return value.isNull();
-}
+template <>
+class ConversionTraits<mbgl::android::Value> {
+public:
+    static bool isUndefined(const mbgl::android::Value& value) {
+        return value.isNull();
+    }
 
-inline bool isArray(const mbgl::android::Value& value) {
-    return value.isArray();
-}
+    static bool isArray(const mbgl::android::Value& value) {
+        return value.isArray();
+    }
 
-inline bool isObject(const mbgl::android::Value& value) {
-    return value.isObject();
-}
+    static bool isObject(const mbgl::android::Value& value) {
+        return value.isObject();
+    }
 
-inline std::size_t arrayLength(const mbgl::android::Value& value) {
-    return value.getLength();;
-}
+    static std::size_t arrayLength(const mbgl::android::Value& value) {
+        return value.getLength();;
+    }
 
-inline mbgl::android::Value arrayMember(const mbgl::android::Value& value, std::size_t i) {
-    return value.get(i);
-}
+    static mbgl::android::Value arrayMember(const mbgl::android::Value& value, std::size_t i) {
+        return value.get(i);
+    }
 
-inline optional<mbgl::android::Value> objectMember(const mbgl::android::Value& value, const char* key) {
-    mbgl::android::Value member = value.get(key);
+    static optional<mbgl::android::Value> objectMember(const mbgl::android::Value& value, const char* key) {
+        mbgl::android::Value member = value.get(key);
+        if (!member.isNull()) {
+            return member;
+        } else {
+            return {};
+        }
+    }
 
-    if (!member.isNull()) {
-        return member;
-    } else {
+    template <class Fn>
+    static optional<Error> eachMember(const mbgl::android::Value&, Fn&&) {
+        // TODO
+        mbgl::Log::Warning(mbgl::Event::Android, "eachMember not implemented");
         return {};
     }
-}
 
-template <class Fn>
-optional<Error> eachMember(const mbgl::android::Value&, Fn&&) {
-    // TODO
-    mbgl::Log::Warning(mbgl::Event::Android, "eachMember not implemented");
-    return {};
-}
+    static optional<bool> toBool(const mbgl::android::Value& value) {
+        if (value.isBool()) {
+            return value.toBool();
+        } else {
+            return {};
+        }
+    }
 
-inline optional<bool> toBool(const mbgl::android::Value& value) {
-    if (value.isBool()) {
-        return value.toBool();
-    } else {
-        return {};
+    static optional<float> toNumber(const mbgl::android::Value& value) {
+        if (value.isNumber()) {
+            auto num = value.toFloat();
+            return num;
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<float> toNumber(const mbgl::android::Value& value) {
-    if (value.isNumber()) {
-        auto num = value.toFloat();
-        return num;
-    } else {
-        return {};
+    static optional<double> toDouble(const mbgl::android::Value& value) {
+        if (value.isNumber()) {
+            return value.toDouble();
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<double> toDouble(const mbgl::android::Value& value) {
-    if (value.isNumber()) {
-        return value.toDouble();
-    } else {
-        return {};
+    static optional<std::string> toString(const mbgl::android::Value& value) {
+        if (value.isString()) {
+            return value.toString();
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<std::string> toString(const mbgl::android::Value& value) {
-    if (value.isString()) {
-        return value.toString();
-    } else {
-        return {};
+    static optional<Value> toValue(const mbgl::android::Value& value) {
+        if (value.isNull()) {
+            return {};
+        } else if (value.isBool()) {
+            return { value.toBool() };
+        } else if (value.isString()) {
+            return { value.toString() };
+        } else if (value.isNumber()) {
+            auto doubleVal = value.toDouble();
+            return { doubleVal - (int) doubleVal > 0.0 ? doubleVal : value.toLong() };
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<Value> toValue(const mbgl::android::Value& value) {
-    if (value.isNull()) {
-        return {};
-    } else if (value.isBool()) {
-        return { value.toBool() };
-    } else if (value.isString()) {
-        return { value.toString() };
-    } else if (value.isNumber()) {
-        auto doubleVal = value.toDouble();
-        return { doubleVal - (int) doubleVal > 0.0 ? doubleVal : value.toLong() };
-    } else {
-        return {};
+    static optional<GeoJSON> toGeoJSON(const mbgl::android::Value &value, Error &error) {
+        if (value.isNull() || !value.isString()) {
+            error = { "no json data found" };
+            return {};
+        }
+        return parseGeoJSON(value.toString(), error);
     }
+};
+
+template <class T, class...Args>
+optional<T> convert(mbgl::android::Value&& value, Error& error, Args&&...args) {
+    return convert<T>(Convertible(std::move(value)), error, std::forward<Args>(args)...);
 }
 
 } // namespace conversion
diff --git a/platform/android/src/style/conversion/filter.hpp b/platform/android/src/style/conversion/filter.hpp
index 1f0abcf3a4..c154e88e7c 100644
--- a/platform/android/src/style/conversion/filter.hpp
+++ b/platform/android/src/style/conversion/filter.hpp
@@ -16,9 +16,8 @@ namespace conversion {
 inline optional<mbgl::style::Filter> toFilter(jni::JNIEnv& env, jni::Array<jni::Object<>> jfilter) {
     mbgl::optional<mbgl::style::Filter> filter;
     if (jfilter) {
-      Value filterValue(env, jfilter);
       mbgl::style::conversion::Error error;
-      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(filterValue, error);
+      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(Value(env, jfilter), error);
       if (!converted) {
           mbgl::Log::Error(mbgl::Event::JNI, "Error converting filter: " + error.message);
       }
diff --git a/platform/android/src/style/conversion/geojson.hpp b/platform/android/src/style/conversion/geojson.hpp
deleted file mode 100644
index 748fe7361e..0000000000
--- a/platform/android/src/style/conversion/geojson.hpp
+++ /dev/null
@@ -1,24 +0,0 @@
-#pragma once
-
-#include <mapbox/geojson.hpp>
-#include <mbgl/style/conversion.hpp>
-#include <mbgl/style/conversion/geojson.hpp>
-#include <jni/jni.hpp>
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template <>
-optional<GeoJSON> Converter<GeoJSON>::operator()(const mbgl::android::Value& value, Error& error) const {
-    if(value.isNull() || !value.isString()) {
-        error = { "no json data found" };
-        return {};
-    }
-
-    return convert<GeoJSON>(value.toString(), error);
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/platform/android/src/style/conversion/url_or_tileset.hpp b/platform/android/src/style/conversion/url_or_tileset.hpp
index 00ef913d41..92c1182a63 100644
--- a/platform/android/src/style/conversion/url_or_tileset.hpp
+++ b/platform/android/src/style/conversion/url_or_tileset.hpp
@@ -17,18 +17,19 @@ 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) {
+inline variant<std::string, Tileset> convertURLOrTileset(mbgl::android::Value&& value) {
     using namespace mbgl::style::conversion;
 
-    if (isObject(value)) {
+    const Convertible convertible(std::move(value));
+    if (isObject(convertible)) {
         Error error;
-        optional<Tileset> tileset = convert<Tileset>(value, error);
+        optional<Tileset> tileset = convert<Tileset>(convertible, error);
         if (!tileset) {
             throw std::logic_error(error.message);
         }
         return { *tileset };
     } else {
-        return { *toString(value) };
+        return { *toString(convertible) };
     }
 }
 
diff --git a/platform/android/src/style/layers/layer.cpp b/platform/android/src/style/layers/layer.cpp
index 02a1f0be82..31032b117f 100644
--- a/platform/android/src/style/layers/layer.cpp
+++ b/platform/android/src/style/layers/layer.cpp
@@ -4,11 +4,20 @@
 #include <jni/jni.hpp>
 
 #include <mbgl/style/style.hpp>
+#include <mbgl/style/filter.hpp>
 #include <mbgl/style/transition_options.hpp>
+#include <mbgl/style/layers/background_layer.hpp>
+#include <mbgl/style/layers/circle_layer.hpp>
+#include <mbgl/style/layers/fill_layer.hpp>
+#include <mbgl/style/layers/fill_extrusion_layer.hpp>
+#include <mbgl/style/layers/line_layer.hpp>
+#include <mbgl/style/layers/raster_layer.hpp>
+#include <mbgl/style/layers/symbol_layer.hpp>
 #include <mbgl/util/logging.hpp>
 
 // Java -> C++ conversion
 #include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/filter.hpp>
 #include <mbgl/style/conversion/layer.hpp>
 #include <mbgl/style/conversion/source.hpp>
 
@@ -78,10 +87,8 @@ namespace android {
     }
 
     void Layer::setLayoutProperty(jni::JNIEnv& env, jni::String jname, jni::Object<> jvalue) {
-        Value value(env, jvalue);
-
         // Convert and set property
-        optional<mbgl::style::conversion::Error> error = mbgl::style::conversion::setLayoutProperty(layer, jni::Make<std::string>(env, jname), value);
+        optional<mbgl::style::conversion::Error> error = mbgl::style::conversion::setLayoutProperty(layer, jni::Make<std::string>(env, jname), Value(env, jvalue));
         if (error) {
             mbgl::Log::Error(mbgl::Event::JNI, "Error setting property: " + jni::Make<std::string>(env, jname) + " " + error->message);
             return;
@@ -89,10 +96,8 @@ namespace android {
     }
 
     void Layer::setPaintProperty(jni::JNIEnv& env, jni::String jname, jni::Object<> jvalue) {
-        Value value(env, jvalue);
-
         // Convert and set property
-        optional<mbgl::style::conversion::Error> error = mbgl::style::conversion::setPaintProperty(layer, jni::Make<std::string>(env, jname), value);
+        optional<mbgl::style::conversion::Error> error = mbgl::style::conversion::setPaintProperty(layer, jni::Make<std::string>(env, jname), Value(env, jvalue));
         if (error) {
             mbgl::Log::Error(mbgl::Event::JNI, "Error setting property: " + jni::Make<std::string>(env, jname) + " " + error->message);
             return;
@@ -116,10 +121,8 @@ namespace android {
         using namespace mbgl::style;
         using namespace mbgl::style::conversion;
 
-        Value wrapped(env, jfilter);
-
         Error error;
-        optional<Filter> converted = convert<Filter>(wrapped, error);
+        optional<Filter> converted = convert<Filter>(Value(env, jfilter), error);
         if (!converted) {
             mbgl::Log::Error(mbgl::Event::JNI, "Error setting filter: " + error.message);
             return;
diff --git a/platform/android/src/style/sources/geojson_source.cpp b/platform/android/src/style/sources/geojson_source.cpp
index 90ef851eba..4468b453f3 100644
--- a/platform/android/src/style/sources/geojson_source.cpp
+++ b/platform/android/src/style/sources/geojson_source.cpp
@@ -5,15 +5,15 @@
 // Java -> C++ conversion
 #include "../android_conversion.hpp"
 #include "../conversion/filter.hpp"
-#include "../conversion/geojson.hpp"
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
+#include <mbgl/style/conversion/geojson_options.hpp>
 
 // C++ -> Java conversion
 #include "../../conversion/conversion.hpp"
 #include "../../conversion/collection.hpp"
 #include "../../geojson/conversion/feature.hpp"
 #include "../conversion/url_or_tileset.hpp"
-#include <mbgl/style/conversion.hpp>
-#include <mbgl/style/conversion/geojson_options.hpp>
 
 #include <string>
 
@@ -29,7 +29,7 @@ namespace android {
             return style::GeoJSONOptions();
         }
         Error error;
-        optional<style::GeoJSONOptions> result = convert<style::GeoJSONOptions>(Value(env, options), error);
+        optional<style::GeoJSONOptions> result = convert<style::GeoJSONOptions>(mbgl::android::Value(env, options), error);
         if (!result) {
             throw std::logic_error(error.message);
         }
@@ -54,7 +54,7 @@ namespace android {
 
         // Convert the jni object
         Error error;
-        optional<GeoJSON> converted = convert<GeoJSON>(Value(env, json), error);
+        optional<GeoJSON> converted = convert<GeoJSON>(mbgl::android::Value(env, json), error);
         if(!converted) {
             mbgl::Log::Error(mbgl::Event::JNI, "Error setting geo json: " + error.message);
             return;
diff --git a/platform/android/src/style/value.cpp b/platform/android/src/style/value.cpp
index e1cd81d7fd..70bdea6677 100644
--- a/platform/android/src/style/value.cpp
+++ b/platform/android/src/style/value.cpp
@@ -24,8 +24,6 @@ namespace android {
 
     Value::Value(jni::JNIEnv& _env, jni::jobject* _value) : env(_env), value(_value, ObjectDeleter(env)) {}
 
-    Value::~Value() = default;
-
     bool Value::isNull() const {
         return value == nullptr;
     }
diff --git a/platform/android/src/style/value.hpp b/platform/android/src/style/value.hpp
index 7464bae832..2057b93454 100644
--- a/platform/android/src/style/value.hpp
+++ b/platform/android/src/style/value.hpp
@@ -9,9 +9,13 @@ namespace android {
 
 class Value {
 public:
-
     Value(jni::JNIEnv&, jni::jobject*);
-    virtual ~Value();
+
+    Value(Value&&)                 = default;
+    Value& operator=(Value&&)      = default;
+
+    Value(const Value&)            = delete;
+    Value& operator=(const Value&) = delete;
 
     bool isNull() const;
     bool isArray() const;
diff --git a/platform/darwin/src/MGLConversion.h b/platform/darwin/src/MGLConversion.h
index d6363b28eb..0d18d4e716 100644
--- a/platform/darwin/src/MGLConversion.h
+++ b/platform/darwin/src/MGLConversion.h
@@ -1,9 +1,4 @@
-#import <Foundation/Foundation.h>
-
-#include <mbgl/util/logging.hpp>
 #include <mbgl/style/conversion.hpp>
-#include <mbgl/util/feature.hpp>
-#include <mbgl/util/optional.hpp>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -11,128 +6,147 @@ namespace mbgl {
 namespace style {
 namespace conversion {
 
-/**
- A minimal wrapper class conforming to the requirements for `objectMember(v, name)` (see mbgl/style/conversion.hpp)
- This is necessary because using `NSObject*` as the value type in `optional<NSObject*>` causes problems for the ARC,
- due to things like `optional(const value_type& __v)`
- */
-class OptionalNSObjectValue {
+// A wrapper class for `id`, so as not to confuse ARC.
+class Holder {
 public:
-    OptionalNSObjectValue(NSObject * _Nullable _value) : value(_value) {}
-    
-    explicit operator bool() const {
-        return value;
+    Holder(const id v) : value(v) {}
+    const id value;
+};
+
+template <>
+class ConversionTraits<Holder> {
+public:
+    static bool isUndefined(const Holder& holder) {
+        const id value = holder.value;
+        return !value || value == [NSNull null];
     }
-    
-    NSObject * _Nullable operator*() {
-        NSCAssert(this, @"Expected non-null value.");
-        return value;
+
+    static bool isArray(const Holder& holder) {
+        const id value = holder.value;
+        return [value isKindOfClass:[NSArray class]];
     }
-private:
-    NSObject * _Nullable value;
-};
 
-inline bool isUndefined(const id value) {
-    return !value || value == [NSNull null];
-}
+    static bool isObject(const Holder& holder) {
+        const id value = holder.value;
+        return [value isKindOfClass:[NSDictionary class]];
+    }
 
-inline bool isArray(const id value) {
-    return [value isKindOfClass:[NSArray class]];
-}
+    static std::size_t arrayLength(const Holder& holder) {
+        const id value = holder.value;
+        NSCAssert([value isKindOfClass:[NSArray class]], @"Value must be an NSArray for getLength().");
+        NSArray *array = value;
+        auto length = [array count];
+        NSCAssert(length <= std::numeric_limits<size_t>::max(), @"Array length out of bounds.");
+        return length;
+    }
 
-inline bool isObject(const id value) {
-    return [value isKindOfClass:[NSDictionary class]];
-}
+    static Holder arrayMember(const Holder& holder, std::size_t i) {
+        const id value = holder.value;
+        NSCAssert([value isKindOfClass:[NSArray class]], @"Value must be an NSArray for get(int).");
+        NSCAssert(i < NSUIntegerMax, @"Index must be less than NSUIntegerMax");
+        return {[value objectAtIndex: i]};
+    }
 
-inline std::size_t arrayLength(const id value) {
-    NSCAssert([value isKindOfClass:[NSArray class]], @"Value must be an NSArray for getLength().");
-    NSArray *array = value;
-    auto length = [array count];
-    NSCAssert(length <= std::numeric_limits<size_t>::max(), @"Array length out of bounds.");
-    return length;
-}
+    static optional<Holder> objectMember(const Holder& holder, const char *key) {
+        const id value = holder.value;
+        NSCAssert([value isKindOfClass:[NSDictionary class]], @"Value must be an NSDictionary for get(string).");
+        NSObject *member = [value objectForKey: @(key)];
+        if (member && member != [NSNull null]) {
+            return {member};
+        } else {
+            return {};
+        }
+    }
 
-inline NSObject *arrayMember(const id value, std::size_t i) {
-    NSCAssert([value isKindOfClass:[NSArray class]], @"Value must be an NSArray for get(int).");
-    NSCAssert(i < NSUIntegerMax, @"Index must be less than NSUIntegerMax");
-    return [value objectAtIndex: i];
-}
+// Compiler is wrong about `Fn` parameter missing a nullability specifier.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnullability-completeness"
+    template <class Fn>
+    static optional<Error> eachMember(const Holder&, Fn&&) {
+#pragma clang diagnostic pop
+        // Not implemented (unneeded for MGLStyleFunction conversion).
+        NSCAssert(NO, @"eachMember not implemented");
+        return {};
+    }
 
-inline OptionalNSObjectValue objectMember(const id value, const char *key) {
-    NSCAssert([value isKindOfClass:[NSDictionary class]], @"Value must be an NSDictionary for get(string).");
-    NSObject *member = [value objectForKey: @(key)];
-    if (member && member != [NSNull null]) {
-        return { member };
-    } else {
-        return { nullptr };
+    static optional<bool> toBool(const Holder& holder) {
+        const id value = holder.value;
+        if (_isBool(value)) {
+            return ((NSNumber *)value).boolValue;
+        } else {
+            return {};
+        }
     }
-}
 
-// Not implemented (unneeded for MGLStyleFunction conversion):
-// optional<Error> eachMember(const NSObject*, Fn&&)
+    static optional<float> toNumber(const Holder& holder) {
+        const id value = holder.value;
+        if (_isNumber(value)) {
+            return ((NSNumber *)value).floatValue;
+        } else {
+            return {};
+        }
+    }
 
-inline bool _isBool(const id value) {
-    if (![value isKindOfClass:[NSNumber class]]) return false;
-    // char: 32-bit boolean
-    // BOOL: 64-bit boolean
-    NSNumber *number = value;
-    return ((strcmp([number objCType], @encode(char)) == 0) ||
-            (strcmp([number objCType], @encode(BOOL)) == 0));
-}
-    
-inline bool _isNumber(const id value) {
-    return [value isKindOfClass:[NSNumber class]] && !_isBool(value);
-}
-    
-inline bool _isString(const id value) {
-    return [value isKindOfClass:[NSString class]];
-}
+    static optional<double> toDouble(const Holder& holder) {
+        const id value = holder.value;
+        if (_isNumber(value)) {
+            return ((NSNumber *)value).doubleValue;
+        } else {
+            return {};
+        }
+    }
 
-inline optional<bool> toBool(const id value) {
-    if (_isBool(value)) {
-        return ((NSNumber *)value).boolValue;
-    } else {
-        return {};
+    static optional<std::string> toString(const Holder& holder) {
+        const id value = holder.value;
+        if (_isString(value)) {
+            return std::string(static_cast<const char *>([value UTF8String]));
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<float> toNumber(const id value) {
-    if (_isNumber(value)) {
-        return ((NSNumber *)value).floatValue;
-    } else {
-        return {};
+    static optional<mbgl::Value> toValue(const Holder& holder) {
+        const id value = holder.value;
+        if (isUndefined(value)) {
+            return {};
+        } else if (_isBool(value)) {
+            return { *toBool(holder) };
+        } else if ( _isString(value)) {
+            return { *toString(holder) };
+        } else if (_isNumber(value)) {
+            // Need to cast to a double here as the float is otherwise considered a bool...
+           return { static_cast<double>(*toNumber(holder)) };
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<double> toDouble(const id value) {
-    if (_isNumber(value)) {
-        return ((NSNumber *)value).doubleValue;
-    } else {
+    static optional<GeoJSON> toGeoJSON(const Holder& holder, Error& error) {
+        error = { "toGeoJSON not implemented" };
         return {};
     }
-}
 
-inline optional<std::string> toString(const id value) {
-    if (_isString(value)) {
-        return std::string(static_cast<const char *>([value UTF8String]));
-    } else {
-        return {};
+private:
+    static bool _isBool(const id value) {
+        if (![value isKindOfClass:[NSNumber class]]) return false;
+        // char: 32-bit boolean
+        // BOOL: 64-bit boolean
+        NSNumber *number = value;
+        return ((strcmp([number objCType], @encode(char)) == 0) ||
+                (strcmp([number objCType], @encode(BOOL)) == 0));
     }
-}
 
-inline optional<mbgl::Value> toValue(const id value) {
-    if (isUndefined(value)) {
-        return {};
-    } else if (_isBool(value)) {
-        return { *toBool(value) };
-    } else if ( _isString(value)) {
-        return { *toString(value) };
-    } else if (_isNumber(value)) {
-        // Need to cast to a double here as the float is otherwise considered a bool...
-       return { static_cast<double>(*toNumber(value)) };
-    } else {
-        return {};
+    static bool _isNumber(const id value) {
+        return [value isKindOfClass:[NSNumber class]] && !_isBool(value);
     }
+
+    static bool _isString(const id value) {
+        return [value isKindOfClass:[NSString class]];
+    }
+};
+
+inline Convertible makeConvertible(const id value) {
+    return Convertible(Holder(value));
 }
 
 } // namespace conversion
@@ -140,4 +154,3 @@ inline optional<mbgl::Value> toValue(const id value) {
 } // namespace mbgl
 
 NS_ASSUME_NONNULL_END
-
diff --git a/platform/darwin/src/MGLStyleValue_Private.h b/platform/darwin/src/MGLStyleValue_Private.h
index 2155c657bd..5914e0a2aa 100644
--- a/platform/darwin/src/MGLStyleValue_Private.h
+++ b/platform/darwin/src/MGLStyleValue_Private.h
@@ -124,9 +124,9 @@ public:
         if ([value isKindOfClass:[MGLConstantStyleValue class]]) {
             return toMBGLConstantValue((MGLConstantStyleValue<ObjCType> *)value);
         } else if ([value isKindOfClass:[MGLStyleFunction class]]) {
-            auto rawValue = toRawStyleSpecValue((MGLStyleFunction<ObjCType> *) value);
             mbgl::style::conversion::Error error;
-            auto result = mbgl::style::conversion::convert<mbgl::style::DataDrivenPropertyValue<MBGLType>>(rawValue, error);
+            auto result = mbgl::style::conversion::convert<mbgl::style::DataDrivenPropertyValue<MBGLType>>(
+                mbgl::style::conversion::makeConvertible(toRawStyleSpecValue((MGLStyleFunction<ObjCType> *) value)), error);
             NSCAssert(result, @(error.message.c_str()));
             return *result;
         } else {
diff --git a/platform/node/src/node_conversion.hpp b/platform/node/src/node_conversion.hpp
index d266745548..7c5bbf4386 100644
--- a/platform/node/src/node_conversion.hpp
+++ b/platform/node/src/node_conversion.hpp
@@ -9,111 +9,136 @@
 #include <mbgl/util/optional.hpp>
 #include <mbgl/util/feature.hpp>
 #include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
-inline bool isUndefined(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    return value->IsUndefined() || value->IsNull();
-}
+template <>
+class ConversionTraits<v8::Local<v8::Value>> {
+public:
+    static bool isUndefined(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsUndefined() || value->IsNull();
+    }
 
-inline bool isArray(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    return value->IsArray();
-}
+    static bool isArray(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsArray();
+    }
 
-inline std::size_t arrayLength(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    return value.As<v8::Array>()->Length();
-}
+    static std::size_t arrayLength(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        // const_cast because v8::Local<T>::As is not marked const until node v8.0
+        v8::Local<v8::Array> array = const_cast<v8::Local<v8::Value>&>(value).As<v8::Array>();
+        return array->Length();
+    }
 
-inline v8::Local<v8::Value> arrayMember(v8::Local<v8::Value> value, std::size_t i) {
-    Nan::EscapableHandleScope scope;
-    return scope.Escape(Nan::Get(value.As<v8::Array>(), i).ToLocalChecked());
-}
+    static v8::Local<v8::Value> arrayMember(const v8::Local<v8::Value>& value, std::size_t i) {
+        Nan::EscapableHandleScope scope;
+        // const_cast because v8::Local<T>::As is not marked const until node v8.0
+        v8::Local<v8::Array> array = const_cast<v8::Local<v8::Value>&>(value).As<v8::Array>();
+        return scope.Escape(Nan::Get(array, i).ToLocalChecked());
+    }
 
-inline bool isObject(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    return value->IsObject() && !value->IsArray();
-}
+    static bool isObject(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsObject() && !value->IsArray();
+    }
 
-inline optional<v8::Local<v8::Value>> objectMember(v8::Local<v8::Value> value, const char * name) {
-    Nan::EscapableHandleScope scope;
-    if (!Nan::Has(Nan::To<v8::Object>(value).ToLocalChecked(), Nan::New(name).ToLocalChecked()).FromJust()) {
-        return {};
+    static optional<v8::Local<v8::Value>> objectMember(const v8::Local<v8::Value>& value, const char * name) {
+        Nan::EscapableHandleScope scope;
+        if (!Nan::Has(Nan::To<v8::Object>(value).ToLocalChecked(), Nan::New(name).ToLocalChecked()).FromJust()) {
+            return {};
+        }
+        Nan::MaybeLocal<v8::Value> result = Nan::Get(Nan::To<v8::Object>(value).ToLocalChecked(), Nan::New(name).ToLocalChecked());
+        if (result.IsEmpty()) {
+            return {};
+        }
+        return {scope.Escape(result.ToLocalChecked())};
     }
-    Nan::MaybeLocal<v8::Value> result = Nan::Get(Nan::To<v8::Object>(value).ToLocalChecked(), Nan::New(name).ToLocalChecked());
-    if (result.IsEmpty()) {
+
+    template <class Fn>
+    static optional<Error> eachMember(const v8::Local<v8::Value>& value, Fn&& fn) {
+        Nan::HandleScope scope;
+        v8::Local<v8::Array> names = Nan::GetOwnPropertyNames(Nan::To<v8::Object>(value).ToLocalChecked()).ToLocalChecked();
+        for (uint32_t i = 0; i < names->Length(); ++i) {
+            v8::Local<v8::Value> k = Nan::Get(names, i).ToLocalChecked();
+            v8::Local<v8::Value> v = Nan::Get(Nan::To<v8::Object>(value).ToLocalChecked(), k).ToLocalChecked();
+            optional<Error> result = fn(*Nan::Utf8String(k), std::move(v));
+            if (result) {
+                return result;
+            }
+        }
         return {};
     }
-    return scope.Escape(result.ToLocalChecked());
-}
 
-template <class Fn>
-optional<Error> eachMember(v8::Local<v8::Value> value, Fn&& fn) {
-    Nan::HandleScope scope;
-    v8::Local<v8::Array> names = Nan::GetOwnPropertyNames(Nan::To<v8::Object>(value).ToLocalChecked()).ToLocalChecked();
-    for (uint32_t i = 0; i < names->Length(); ++i) {
-        v8::Local<v8::Value> k = Nan::Get(names, i).ToLocalChecked();
-        v8::Local<v8::Value> v = Nan::Get(Nan::To<v8::Object>(value).ToLocalChecked(), k).ToLocalChecked();
-        optional<Error> result = fn(*Nan::Utf8String(k), v);
-        if (result) {
-            return result;
+    static optional<bool> toBool(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsBoolean()) {
+            return {};
         }
+        return value->BooleanValue();
     }
-    return {};
-}
 
-inline optional<bool> toBool(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    if (!value->IsBoolean()) {
-        return {};
+    static optional<float> toNumber(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->NumberValue();
     }
-    return value->BooleanValue();
-}
 
-inline optional<float> toNumber(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    if (!value->IsNumber()) {
-        return {};
+    static optional<double> toDouble(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->NumberValue();
     }
-    return value->NumberValue();
-}
 
-inline optional<double> toDouble(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    if (!value->IsNumber()) {
-        return {};
+    static optional<std::string> toString(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsString()) {
+            return {};
+        }
+        return std::string(*Nan::Utf8String(value));
     }
-    return value->NumberValue();
-}
 
-inline optional<std::string> toString(v8::Local<v8::Value> value) {
-    Nan::HandleScope scope;
-    if (!value->IsString()) {
-        return {};
+    static optional<Value> toValue(const v8::Local<v8::Value>& value) {
+        if (value->IsFalse()) {
+            return { false };
+        } else if (value->IsTrue()) {
+            return { true };
+        } else if (value->IsString()) {
+            return { std::string(*Nan::Utf8String(value)) };
+        } else if (value->IsUint32()) {
+            return { std::uint64_t(value->Uint32Value()) };
+        } else if (value->IsInt32()) {
+            return { std::int64_t(value->Int32Value()) };
+        } else if (value->IsNumber()) {
+            return { value->NumberValue() };
+        } else {
+            return {};
+        }
     }
-    return std::string(*Nan::Utf8String(value));
-}
 
-inline optional<Value> toValue(v8::Local<v8::Value> value) {
-    if (value->IsFalse()) {
-        return { false };
-    } else if (value->IsTrue()) {
-        return { true };
-    } else if (value->IsString()) {
-        return { std::string(*Nan::Utf8String(value)) };
-    } else if (value->IsUint32()) {
-        return { std::uint64_t(value->Uint32Value()) };
-    } else if (value->IsInt32()) {
-        return { std::int64_t(value->Int32Value()) };
-    } else if (value->IsNumber()) {
-        return { value->NumberValue() };
-    } else {
-        return {};
+    static optional<GeoJSON> toGeoJSON(const v8::Local<v8::Value>& value, Error& error) {
+        try {
+            Nan::JSON JSON;
+            std::string string = *Nan::Utf8String(JSON.Stringify(value->ToObject()).ToLocalChecked());
+            return parseGeoJSON(string, error);
+        } catch (const std::exception& ex) {
+            error = { ex.what() };
+            return {};
+        }
     }
+};
+
+template <class T, class...Args>
+optional<T> convert(const v8::Local<v8::Value>& value, Error& error, Args&&...args) {
+    return convert<T>(Convertible(value), error, std::forward<Args>(args)...);
 }
 
 } // namespace conversion
diff --git a/platform/node/src/node_geojson.hpp b/platform/node/src/node_geojson.hpp
deleted file mode 100644
index 8a3927e2cf..0000000000
--- a/platform/node/src/node_geojson.hpp
+++ /dev/null
@@ -1,17 +0,0 @@
-#include <mbgl/style/conversion/geojson.hpp>
-
-#include <string>
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template <>
-optional<GeoJSON> Converter<GeoJSON>::operator()(const v8::Local<v8::Value>& value, Error& error) const {
-    Nan::JSON JSON;
-    std::string string = *Nan::Utf8String(JSON.Stringify(value->ToObject()).ToLocalChecked());
-    return convert<GeoJSON>(string, error);
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/platform/node/src/node_map.cpp b/platform/node/src/node_map.cpp
index f344461f31..6deccf05bf 100644
--- a/platform/node/src/node_map.cpp
+++ b/platform/node/src/node_map.cpp
@@ -2,7 +2,6 @@
 #include "node_request.hpp"
 #include "node_feature.hpp"
 #include "node_conversion.hpp"
-#include "node_geojson.hpp"
 
 #include <mbgl/util/exception.hpp>
 #include <mbgl/renderer/renderer.hpp>
@@ -10,6 +9,15 @@
 #include <mbgl/style/conversion/source.hpp>
 #include <mbgl/style/conversion/layer.hpp>
 #include <mbgl/style/conversion/filter.hpp>
+
+#include <mbgl/style/layers/background_layer.hpp>
+#include <mbgl/style/layers/circle_layer.hpp>
+#include <mbgl/style/layers/fill_layer.hpp>
+#include <mbgl/style/layers/fill_extrusion_layer.hpp>
+#include <mbgl/style/layers/line_layer.hpp>
+#include <mbgl/style/layers/raster_layer.hpp>
+#include <mbgl/style/layers/symbol_layer.hpp>
+
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/image.hpp>
 #include <mbgl/map/map_observer.hpp>
@@ -741,7 +749,7 @@ void NodeMap::SetLayoutProperty(const Nan::FunctionCallbackInfo<v8::Value>& info
         return Nan::ThrowTypeError("Second argument must be a string");
     }
 
-    mbgl::optional<Error> error = setLayoutProperty(*layer, *Nan::Utf8String(info[1]), info[2]);
+    mbgl::optional<Error> error = setLayoutProperty(*layer, *Nan::Utf8String(info[1]), Convertible(info[2]));
     if (error) {
         return Nan::ThrowTypeError(error->message.c_str());
     }
@@ -773,7 +781,7 @@ void NodeMap::SetPaintProperty(const Nan::FunctionCallbackInfo<v8::Value>& info)
         return Nan::ThrowTypeError("Second argument must be a string");
     }
 
-    mbgl::optional<Error> error = setPaintProperty(*layer, *Nan::Utf8String(info[1]), info[2]);
+    mbgl::optional<Error> error = setPaintProperty(*layer, *Nan::Utf8String(info[1]), Convertible(info[2]));
     if (error) {
         return Nan::ThrowTypeError(error->message.c_str());
     }
diff --git a/platform/qt/qt.cmake b/platform/qt/qt.cmake
index 2346d7d820..a7862c3936 100644
--- a/platform/qt/qt.cmake
+++ b/platform/qt/qt.cmake
@@ -60,6 +60,9 @@ set(MBGL_QT_FILESOURCE_FILES
 add_library(qmapboxgl SHARED
     platform/qt/include/qmapbox.hpp
     platform/qt/include/qmapboxgl.hpp
+    platform/qt/src/qt_conversion.hpp
+    platform/qt/src/qt_geojson.cpp
+    platform/qt/src/qt_geojson.hpp
     platform/qt/src/qmapbox.cpp
     platform/qt/src/qmapboxgl.cpp
     platform/qt/src/qmapboxgl_p.hpp
diff --git a/platform/qt/src/qmapboxgl.cpp b/platform/qt/src/qmapboxgl.cpp
index 074ef280aa..740bb90202 100644
--- a/platform/qt/src/qmapboxgl.cpp
+++ b/platform/qt/src/qmapboxgl.cpp
@@ -14,7 +14,17 @@
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/layer.hpp>
 #include <mbgl/style/conversion/source.hpp>
+#include <mbgl/style/conversion/filter.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
+#include <mbgl/style/filter.hpp>
 #include <mbgl/style/layers/custom_layer.hpp>
+#include <mbgl/style/layers/background_layer.hpp>
+#include <mbgl/style/layers/circle_layer.hpp>
+#include <mbgl/style/layers/fill_layer.hpp>
+#include <mbgl/style/layers/fill_extrusion_layer.hpp>
+#include <mbgl/style/layers/line_layer.hpp>
+#include <mbgl/style/layers/raster_layer.hpp>
+#include <mbgl/style/layers/symbol_layer.hpp>
 #include <mbgl/style/sources/geojson_source.hpp>
 #include <mbgl/style/transition_options.hpp>
 #include <mbgl/style/image.hpp>
diff --git a/platform/qt/src/qt_conversion.hpp b/platform/qt/src/qt_conversion.hpp
index 40d7e5b928..19b0cb54fc 100644
--- a/platform/qt/src/qt_conversion.hpp
+++ b/platform/qt/src/qt_conversion.hpp
@@ -1,120 +1,145 @@
 #pragma once
 
 #include <mbgl/style/conversion.hpp>
-#include <mbgl/util/feature.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
 #include <mbgl/util/optional.hpp>
 
-#include <QMapbox>
-
-#include <QColor>
 #include <QVariant>
+#include <QColor>
+#include <QMapbox>
+#include "qt_geojson.hpp"
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
-inline bool isUndefined(const QVariant& value) {
-    return value.isNull() || !value.isValid();
-}
+template <>
+class ConversionTraits<QVariant> {
+public:
+    static bool isUndefined(const QVariant& value) {
+        return value.isNull() || !value.isValid();
+    }
 
-inline bool isArray(const QVariant& value) {
-    return value.canConvert(QVariant::List);
-}
+    static bool isArray(const QVariant& value) {
+        return value.canConvert(QVariant::List);
+    }
 
-inline std::size_t arrayLength(const QVariant& value) {
-    return value.toList().size();
-}
+    static std::size_t arrayLength(const QVariant& value) {
+        return value.toList().size();
+    }
 
-inline QVariant arrayMember(const QVariant& value, std::size_t i) {
-    return value.toList()[i];
-}
+    static QVariant arrayMember(const QVariant& value, std::size_t i) {
+        return value.toList()[i];
+    }
 
-inline bool isObject(const QVariant& value) {
-    return value.canConvert(QVariant::Map)
-        || value.type() == QVariant::ByteArray
-#if QT_VERSION >= 0x050000
-        || QString(value.typeName()) == QStringLiteral("QMapbox::Feature");
-#else
-        || QString(value.typeName()) == QString("QMapbox::Feature");
-#endif
-}
+    static bool isObject(const QVariant& value) {
+        return value.canConvert(QVariant::Map)
+            || value.type() == QVariant::ByteArray
+    #if QT_VERSION >= 0x050000
+            || QString(value.typeName()) == QStringLiteral("QMapbox::Feature");
+    #else
+            || QString(value.typeName()) == QString("QMapbox::Feature");
+    #endif
+    }
 
-inline optional<QVariant> objectMember(const QVariant& value, const char* key) {
-    auto map = value.toMap();
-    auto iter = map.constFind(key);
+    static optional<QVariant> objectMember(const QVariant& value, const char* key) {
+        auto map = value.toMap();
+        auto iter = map.constFind(key);
 
-    if (iter != map.constEnd()) {
-        return iter.value();
-    } else {
-        return {};
+        if (iter != map.constEnd()) {
+            return iter.value();
+        } else {
+            return {};
+        }
     }
-}
 
-using EachMemberFn = std::function<optional<Error>(const std::string&, const QVariant&)>;
+    template <class Fn>
+    static optional<Error> eachMember(const QVariant& value, Fn&& fn) {
+        auto map = value.toMap();
+        auto iter = map.constBegin();
 
-optional<Error> eachMember(const QVariant& value, EachMemberFn&& fn) {
-    auto map = value.toMap();
-    auto iter = map.constBegin();
+        while (iter != map.constEnd()) {
+            optional<Error> result = fn(iter.key().toStdString(), QVariant(iter.value()));
+            if (result) {
+                return result;
+            }
 
-    while (iter != map.constEnd()) {
-        optional<Error> result = fn(iter.key().toStdString(), iter.value());
-        if (result) {
-            return result;
+            ++iter;
         }
 
-        ++iter;
+        return {};
     }
 
-    return {};
-}
+    static optional<bool> toBool(const QVariant& value) {
+        if (value.type() == QVariant::Bool) {
+            return value.toBool();
+        } else {
+            return {};
+        }
+    }
 
-inline optional<bool> toBool(const QVariant& value) {
-    if (value.type() == QVariant::Bool) {
-        return value.toBool();
-    } else {
-        return {};
+    static optional<float> toNumber(const QVariant& value) {
+        if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
+            return value.toFloat();
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<float> toNumber(const QVariant& value) {
-    if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
-        return value.toFloat();
-    } else {
-        return {};
+    static optional<double> toDouble(const QVariant& value) {
+        if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
+            return value.toDouble();
+        } else {
+            return {};
+        }
     }
-}
-inline optional<double> toDouble(const QVariant& value) {
-    if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
-        return value.toDouble();
-    } else {
-        return {};
+
+    static optional<std::string> toString(const QVariant& value) {
+        if (value.type() == QVariant::String) {
+            return value.toString().toStdString();
+        } else if (value.type() == QVariant::Color) {
+            return value.value<QColor>().name().toStdString();
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<std::string> toString(const QVariant& value) {
-    if (value.type() == QVariant::String) {
-        return value.toString().toStdString();
-    } else if (value.type() == QVariant::Color) {
-        return value.value<QColor>().name().toStdString();
-    } else {
-        return {};
+    static optional<Value> toValue(const QVariant& value) {
+        if (value.type() == QVariant::Bool) {
+            return { value.toBool() };
+        } else if (value.type() == QVariant::String) {
+            return { value.toString().toStdString() };
+        } else if (value.type() == QVariant::Color) {
+            return { value.value<QColor>().name().toStdString() };
+        } else if (value.type() == QVariant::Int) {
+            return { int64_t(value.toInt()) };
+        } else if (value.canConvert(QVariant::Double)) {
+            return { value.toDouble() };
+        } else {
+            return {};
+        }
     }
-}
 
-inline optional<Value> toValue(const QVariant& value) {
-    if (value.type() == QVariant::Bool) {
-        return { value.toBool() };
-    } else if (value.type() == QVariant::String) {
-        return { value.toString().toStdString() };
-    } else if (value.type() == QVariant::Color) {
-        return { value.value<QColor>().name().toStdString() };
-    } else if (value.type() == QVariant::Int) {
-        return { int64_t(value.toInt()) };
-    } else if (value.canConvert(QVariant::Double)) {
-        return { value.toDouble() };
-    } else {
-        return {};
+    static optional<GeoJSON> toGeoJSON(const QVariant& value, Error& error) {
+    #if QT_VERSION >= 0x050000
+        if (value.typeName() == QStringLiteral("QMapbox::Feature")) {
+    #else
+        if (value.typeName() == QString("QMapbox::Feature")) {
+    #endif
+            return GeoJSON { asMapboxGLFeature(value.value<QMapbox::Feature>()) };
+        } else if (value.type() != QVariant::ByteArray) {
+            error = { "JSON data must be in QByteArray" };
+            return {};
+        }
+
+        QByteArray data = value.toByteArray();
+        return parseGeoJSON(std::string(data.constData(), data.size()), error);
     }
+};
+
+template <class T, class...Args>
+optional<T> convert(const QVariant& value, Error& error, Args&&...args) {
+    return convert<T>(Convertible(value), error, std::forward<Args>(args)...);
 }
 
 } // namespace conversion
diff --git a/platform/qt/src/qt_geojson.cpp b/platform/qt/src/qt_geojson.cpp
new file mode 100644
index 0000000000..80377de64d
--- /dev/null
+++ b/platform/qt/src/qt_geojson.cpp
@@ -0,0 +1,166 @@
+#include "qt_geojson.hpp"
+#include <mapbox/geojson.hpp>
+#include <mbgl/util/geometry.hpp>
+#include <mbgl/util/feature.hpp>
+
+namespace QMapbox {
+
+mbgl::Point<double> asMapboxGLPoint(const QMapbox::Coordinate &coordinate) {
+    return mbgl::Point<double> { coordinate.second, coordinate.first };
+}
+
+mbgl::MultiPoint<double> asMapboxGLMultiPoint(const QMapbox::Coordinates &multiPoint) {
+    mbgl::MultiPoint<double> mbglMultiPoint;
+    mbglMultiPoint.reserve(multiPoint.size());
+    for (const auto &point: multiPoint) {
+        mbglMultiPoint.emplace_back(asMapboxGLPoint(point));
+    }
+    return mbglMultiPoint;
+};
+
+mbgl::LineString<double> asMapboxGLLineString(const QMapbox::Coordinates &lineString) {
+    mbgl::LineString<double> mbglLineString;
+    mbglLineString.reserve(lineString.size());
+    for (const auto &coordinate : lineString) {
+        mbglLineString.emplace_back(asMapboxGLPoint(coordinate));
+    }
+    return mbglLineString;
+};
+
+mbgl::MultiLineString<double> asMapboxGLMultiLineString(const QMapbox::CoordinatesCollection &multiLineString) {
+    mbgl::MultiLineString<double> mbglMultiLineString;
+    mbglMultiLineString.reserve(multiLineString.size());
+    for (const auto &lineString : multiLineString) {
+        mbglMultiLineString.emplace_back(std::forward<mbgl::LineString<double>>(asMapboxGLLineString(lineString)));
+    }
+    return mbglMultiLineString;
+};
+
+mbgl::Polygon<double> asMapboxGLPolygon(const QMapbox::CoordinatesCollection &polygon) {
+    mbgl::Polygon<double> mbglPolygon;
+    mbglPolygon.reserve(polygon.size());
+    for (const auto &linearRing : polygon) {
+        mbgl::LinearRing<double> mbglLinearRing;
+        mbglLinearRing.reserve(linearRing.size());
+        for (const auto &coordinate: linearRing) {
+            mbglLinearRing.emplace_back(asMapboxGLPoint(coordinate));
+        }
+        mbglPolygon.emplace_back(std::move(mbglLinearRing));
+    }
+    return mbglPolygon;
+};
+
+mbgl::MultiPolygon<double> asMapboxGLMultiPolygon(const QMapbox::CoordinatesCollections &multiPolygon) {
+    mbgl::MultiPolygon<double> mbglMultiPolygon;
+    mbglMultiPolygon.reserve(multiPolygon.size());
+    for (const auto &polygon : multiPolygon) {
+        mbglMultiPolygon.emplace_back(std::forward<mbgl::Polygon<double>>(asMapboxGLPolygon(polygon)));
+    }
+    return mbglMultiPolygon;
+};
+
+mbgl::Value asMapboxGLPropertyValue(const QVariant &value) {
+    auto valueList = [](const QVariantList &list) {
+        std::vector<mbgl::Value> mbglList;
+        mbglList.reserve(list.size());
+        for (const auto& listValue : list) {
+            mbglList.emplace_back(asMapboxGLPropertyValue(listValue));
+        }
+        return mbglList;
+    };
+
+    auto valueMap = [](const QVariantMap &map) {
+        std::unordered_map<std::string, mbgl::Value> mbglMap;
+        mbglMap.reserve(map.size());
+        auto it = map.constBegin();
+        while (it != map.constEnd()) {
+            mbglMap.emplace(std::make_pair(it.key().toStdString(), asMapboxGLPropertyValue(it.value())));
+            ++it;
+        }
+        return mbglMap;
+    };
+
+    switch (value.type()) {
+#if QT_VERSION >= 0x050000
+    case QMetaType::UnknownType:
+#else
+    case QVariant::Invalid:
+#endif
+        return mbgl::NullValue {};
+    case QMetaType::Bool:
+        return { value.toBool() };
+    case QMetaType::ULongLong:
+        return { uint64_t(value.toULongLong()) };
+    case QMetaType::LongLong:
+        return { int64_t(value.toLongLong()) };
+    case QMetaType::Double:
+        return { value.toDouble() };
+    case QMetaType::QString:
+        return { value.toString().toStdString() };
+    case QMetaType::QVariantList:
+        return valueList(value.toList());
+    case QMetaType::QVariantMap:
+        return valueMap(value.toMap());
+    default:
+        qWarning() << "Unsupported feature property value:" << value;
+        return {};
+    }
+}
+
+mbgl::FeatureIdentifier asMapboxGLFeatureIdentifier(const QVariant &id) {
+    switch (id.type()) {
+#if QT_VERSION >= 0x050000
+    case QMetaType::UnknownType:
+#else
+    case QVariant::Invalid:
+#endif
+        return {};
+    case QMetaType::ULongLong:
+        return { uint64_t(id.toULongLong()) };
+    case QMetaType::LongLong:
+        return { int64_t(id.toLongLong()) };
+    case QMetaType::Double:
+        return { id.toDouble() };
+    case QMetaType::QString:
+        return { id.toString().toStdString() };
+    default:
+        qWarning() << "Unsupported feature identifier:" << id;
+        return {};
+    }
+}
+
+mbgl::Feature asMapboxGLFeature(const QMapbox::Feature &feature) {
+    mbgl::PropertyMap properties;
+    properties.reserve(feature.properties.size());
+    auto it = feature.properties.constBegin();
+    while (it != feature.properties.constEnd()) {
+        properties.emplace(std::make_pair(it.key().toStdString(), asMapboxGLPropertyValue(it.value())));
+    }
+
+    mbgl::FeatureIdentifier id = asMapboxGLFeatureIdentifier(feature.id);
+
+    if (feature.type == QMapbox::Feature::PointType) {
+        const QMapbox::Coordinates &points = feature.geometry.first().first();
+        if (points.size() == 1) {
+            return { asMapboxGLPoint(points.first()), std::move(properties), std::move(id) };
+        } else {
+            return { asMapboxGLMultiPoint(points), std::move(properties), std::move(id) };
+        }
+    } else if (feature.type == QMapbox::Feature::LineStringType) {
+        const QMapbox::CoordinatesCollection &lineStrings = feature.geometry.first();
+        if (lineStrings.size() == 1) {
+            return { asMapboxGLLineString(lineStrings.first()), std::move(properties), std::move(id) };
+        } else {
+            return { asMapboxGLMultiLineString(lineStrings), std::move(properties), std::move(id) };
+        }
+    } else { // PolygonType
+        const QMapbox::CoordinatesCollections &polygons = feature.geometry;
+        if (polygons.size() == 1) {
+            return { asMapboxGLPolygon(polygons.first()), std::move(properties), std::move(id) };
+        } else {
+            return { asMapboxGLMultiPolygon(polygons), std::move(properties), std::move(id) };
+        }
+    }
+};
+
+} // namespace QMapbox
diff --git a/platform/qt/src/qt_geojson.hpp b/platform/qt/src/qt_geojson.hpp
index a6958b7edc..a9c10272ab 100644
--- a/platform/qt/src/qt_geojson.hpp
+++ b/platform/qt/src/qt_geojson.hpp
@@ -1,7 +1,8 @@
 #pragma once
 
 #include <mapbox/geojson.hpp>
-#include <mbgl/style/conversion/geojson.hpp>
+#include <mbgl/util/geometry.hpp>
+#include <mbgl/util/feature.hpp>
 
 #include <QMapbox>
 
@@ -13,187 +14,14 @@
 
 namespace QMapbox {
 
-mbgl::Point<double> asMapboxGLPoint(const QMapbox::Coordinate &coordinate) {
-    return mbgl::Point<double> { coordinate.second, coordinate.first };
-}
-
-mbgl::MultiPoint<double> asMapboxGLMultiPoint(const QMapbox::Coordinates &multiPoint) {
-    mbgl::MultiPoint<double> mbglMultiPoint;
-    mbglMultiPoint.reserve(multiPoint.size());
-    for (const auto &point: multiPoint) {
-        mbglMultiPoint.emplace_back(asMapboxGLPoint(point));
-    }
-    return mbglMultiPoint;
-};
-
-mbgl::LineString<double> asMapboxGLLineString(const QMapbox::Coordinates &lineString) {
-    mbgl::LineString<double> mbglLineString;
-    mbglLineString.reserve(lineString.size());
-    for (const auto &coordinate : lineString) {
-        mbglLineString.emplace_back(asMapboxGLPoint(coordinate));
-    }
-    return mbglLineString;
-};
-
-mbgl::MultiLineString<double> asMapboxGLMultiLineString(const QMapbox::CoordinatesCollection &multiLineString) {
-    mbgl::MultiLineString<double> mbglMultiLineString;
-    mbglMultiLineString.reserve(multiLineString.size());
-    for (const auto &lineString : multiLineString) {
-        mbglMultiLineString.emplace_back(std::forward<mbgl::LineString<double>>(asMapboxGLLineString(lineString)));
-    }
-    return mbglMultiLineString;
-};
-
-mbgl::Polygon<double> asMapboxGLPolygon(const QMapbox::CoordinatesCollection &polygon) {
-    mbgl::Polygon<double> mbglPolygon;
-    mbglPolygon.reserve(polygon.size());
-    for (const auto &linearRing : polygon) {
-        mbgl::LinearRing<double> mbglLinearRing;
-        mbglLinearRing.reserve(linearRing.size());
-        for (const auto &coordinate: linearRing) {
-            mbglLinearRing.emplace_back(asMapboxGLPoint(coordinate));
-        }
-        mbglPolygon.emplace_back(std::move(mbglLinearRing));
-    }
-    return mbglPolygon;
-};
-
-mbgl::MultiPolygon<double> asMapboxGLMultiPolygon(const QMapbox::CoordinatesCollections &multiPolygon) {
-    mbgl::MultiPolygon<double> mbglMultiPolygon;
-    mbglMultiPolygon.reserve(multiPolygon.size());
-    for (const auto &polygon : multiPolygon) {
-        mbglMultiPolygon.emplace_back(std::forward<mbgl::Polygon<double>>(asMapboxGLPolygon(polygon)));
-    }
-    return mbglMultiPolygon;
-};
-
-mbgl::Value asMapboxGLPropertyValue(const QVariant &value) {
-    auto valueList = [](const QVariantList &list) {
-        std::vector<mbgl::Value> mbglList;
-        mbglList.reserve(list.size());
-        for (const auto& listValue : list) {
-            mbglList.emplace_back(asMapboxGLPropertyValue(listValue));
-        }
-        return mbglList;
-    };
-
-    auto valueMap = [](const QVariantMap &map) {
-        std::unordered_map<std::string, mbgl::Value> mbglMap;
-        mbglMap.reserve(map.size());
-        auto it = map.constBegin();
-        while (it != map.constEnd()) {
-            mbglMap.emplace(std::make_pair(it.key().toStdString(), asMapboxGLPropertyValue(it.value())));
-            ++it;
-        }
-        return mbglMap;
-    };
-
-    switch (value.type()) {
-#if QT_VERSION >= 0x050000
-    case QMetaType::UnknownType:
-#else
-    case QVariant::Invalid:
-#endif
-        return mbgl::NullValue {};
-    case QMetaType::Bool:
-        return { value.toBool() };
-    case QMetaType::ULongLong:
-        return { uint64_t(value.toULongLong()) };
-    case QMetaType::LongLong:
-        return { int64_t(value.toLongLong()) };
-    case QMetaType::Double:
-        return { value.toDouble() };
-    case QMetaType::QString:
-        return { value.toString().toStdString() };
-    case QMetaType::QVariantList:
-        return valueList(value.toList());
-    case QMetaType::QVariantMap:
-        return valueMap(value.toMap());
-    default:
-        qWarning() << "Unsupported feature property value:" << value;
-        return {};
-    }
-}
-
-mbgl::FeatureIdentifier asMapboxGLFeatureIdentifier(const QVariant &id) {
-    switch (id.type()) {
-#if QT_VERSION >= 0x050000
-    case QMetaType::UnknownType:
-#else
-    case QVariant::Invalid:
-#endif
-        return {};
-    case QMetaType::ULongLong:
-        return { uint64_t(id.toULongLong()) };
-    case QMetaType::LongLong:
-        return { int64_t(id.toLongLong()) };
-    case QMetaType::Double:
-        return { id.toDouble() };
-    case QMetaType::QString:
-        return { id.toString().toStdString() };
-    default:
-        qWarning() << "Unsupported feature identifier:" << id;
-        return {};
-    }
-}
-
-mbgl::Feature asMapboxGLFeature(const QMapbox::Feature &feature) {
-    mbgl::PropertyMap properties;
-    properties.reserve(feature.properties.size());
-    auto it = feature.properties.constBegin();
-    while (it != feature.properties.constEnd()) {
-        properties.emplace(std::make_pair(it.key().toStdString(), asMapboxGLPropertyValue(it.value())));
-    }
-
-    mbgl::FeatureIdentifier id = asMapboxGLFeatureIdentifier(feature.id);
-
-    if (feature.type == QMapbox::Feature::PointType) {
-        const QMapbox::Coordinates &points = feature.geometry.first().first();
-        if (points.size() == 1) {
-            return { asMapboxGLPoint(points.first()), std::move(properties), std::move(id) };
-        } else {
-            return { asMapboxGLMultiPoint(points), std::move(properties), std::move(id) };
-        }
-    } else if (feature.type == QMapbox::Feature::LineStringType) {
-        const QMapbox::CoordinatesCollection &lineStrings = feature.geometry.first();
-        if (lineStrings.size() == 1) {
-            return { asMapboxGLLineString(lineStrings.first()), std::move(properties), std::move(id) };
-        } else {
-            return { asMapboxGLMultiLineString(lineStrings), std::move(properties), std::move(id) };
-        }
-    } else { // PolygonType
-        const QMapbox::CoordinatesCollections &polygons = feature.geometry;
-        if (polygons.size() == 1) {
-            return { asMapboxGLPolygon(polygons.first()), std::move(properties), std::move(id) };
-        } else {
-            return { asMapboxGLMultiPolygon(polygons), std::move(properties), std::move(id) };
-        }
-    }
-};
+mbgl::Point<double> asMapboxGLPoint(const QMapbox::Coordinate &coordinate);
+mbgl::MultiPoint<double> asMapboxGLMultiPoint(const QMapbox::Coordinates &multiPoint);
+mbgl::LineString<double> asMapboxGLLineString(const QMapbox::Coordinates &lineString);
+mbgl::MultiLineString<double> asMapboxGLMultiLineString(const QMapbox::CoordinatesCollection &multiLineString);
+mbgl::Polygon<double> asMapboxGLPolygon(const QMapbox::CoordinatesCollection &polygon);
+mbgl::MultiPolygon<double> asMapboxGLMultiPolygon(const QMapbox::CoordinatesCollections &multiPolygon);
+mbgl::Value asMapboxGLPropertyValue(const QVariant &value);
+mbgl::FeatureIdentifier asMapboxGLFeatureIdentifier(const QVariant &id);
+mbgl::Feature asMapboxGLFeature(const QMapbox::Feature &feature);
 
 } // namespace QMapbox
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template <>
-optional<GeoJSON> Converter<GeoJSON>::operator()(const QVariant& value, Error& error) const {
-#if QT_VERSION >= 0x050000
-    if (value.typeName() == QStringLiteral("QMapbox::Feature")) {
-#else
-    if (value.typeName() == QString("QMapbox::Feature")) {
-#endif
-        return GeoJSON { asMapboxGLFeature(value.value<QMapbox::Feature>()) };
-    } else if (value.type() != QVariant::ByteArray) {
-        error = { "JSON data must be in QByteArray" };
-        return {};
-    }
-
-    QByteArray data = value.toByteArray();
-    return convert<GeoJSON>(std::string(data.constData(), data.size()), error);
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl