Require explicit specialization for ValueTraits

* Allows using more natural types for the trait method inputs (`const JSValue*` instead of `const JSValue* const&`)
* Makes it a compile error rather than a link error if you pass the wrong type to the templated Value constructor
* Allows the compiler to inline the trait methods into the vtable

17 files changed, 591 insertions, 678 deletions

diff --git a/cmake/core-files.cmake b/cmake/core-files.cmake
index cbb0d0e625..7621283e7e 100644
--- a/cmake/core-files.cmake
+++ b/cmake/core-files.cmake
@@ -350,7 +350,6 @@ set(MBGL_CORE_FILES
     src/mbgl/style/parser.cpp
     src/mbgl/style/parser.hpp
     src/mbgl/style/properties.hpp
-    src/mbgl/style/rapidjson_conversion.cpp
     src/mbgl/style/rapidjson_conversion.hpp
     src/mbgl/style/source.cpp
     src/mbgl/style/source_impl.cpp
diff --git a/cmake/node.cmake b/cmake/node.cmake
index 575f45020a..388a98b68f 100644
--- a/cmake/node.cmake
+++ b/cmake/node.cmake
@@ -14,7 +14,6 @@ target_sources(mbgl-node
     PRIVATE platform/node/src/node_logging.hpp
     PRIVATE platform/node/src/node_logging.cpp
     PRIVATE platform/node/src/node_conversion.hpp
-    PRIVATE platform/node/src/node_conversion.cpp
     PRIVATE platform/node/src/node_map.hpp
     PRIVATE platform/node/src/node_map.cpp
     PRIVATE platform/node/src/node_request.hpp
diff --git a/include/mbgl/style/conversion.hpp b/include/mbgl/style/conversion.hpp
index 41034c8a33..3fe7bbe508 100644
--- a/include/mbgl/style/conversion.hpp
+++ b/include/mbgl/style/conversion.hpp
@@ -33,21 +33,7 @@ namespace conversion {
 struct Error { std::string message; };
 
 template <typename T>
-struct ValueTraits {
-    static bool isUndefined(const T& value);
-    static bool isArray(const T& value);
-    static std::size_t arrayLength(const T& value);
-    static T arrayMember(const T& value, std::size_t i);
-    static bool isObject(const T& value);
-    static optional<T> objectMember(const T& value, const char * name);
-    static optional<Error> eachMember(const T& value, const std::function<optional<Error> (const std::string&, const T&)>& fn);
-    static optional<bool> toBool(const T& value);
-    static optional<float> toNumber(const T& value);
-    static optional<double> toDouble(const T& value);
-    static optional<std::string> toString(const T& value);
-    static optional<mbgl::Value> toValue(const T& value);
-    static optional<GeoJSON> toGeoJSON(const T& value, Error& error);
-};
+class ValueTraits;
 
 class Value {
 public:
diff --git a/platform/android/config.cmake b/platform/android/config.cmake
index da752e4cb8..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/android_conversion.cpp
     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.cpp b/platform/android/src/style/android_conversion.cpp
deleted file mode 100644
index 43940c2acd..0000000000
--- a/platform/android/src/style/android_conversion.cpp
+++ /dev/null
@@ -1,106 +0,0 @@
-#include "android_conversion.hpp"
-#include <mbgl/style/conversion/geojson.hpp>
-
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-using AndroidValue = mbgl::android::Value;
-
-template<> bool ValueTraits<AndroidValue>::isUndefined(const AndroidValue& value) {
-    return value.isNull();
-}
-
-template<> bool ValueTraits<AndroidValue>::isArray(const AndroidValue& value) {
-    return value.isArray();
-}
-
-template<> bool ValueTraits<AndroidValue>::isObject(const AndroidValue& value) {
-    return value.isObject();
-}
-
-template<> std::size_t ValueTraits<AndroidValue>::arrayLength(const AndroidValue& value) {
-    return value.getLength();;
-}
-
-template<> AndroidValue ValueTraits<AndroidValue>::arrayMember(const AndroidValue& value, std::size_t i) {
-    return value.get(i);
-}
-
-template<> optional<AndroidValue> ValueTraits<AndroidValue>::objectMember(const AndroidValue& value, const char* key) {
-    AndroidValue member = value.get(key);
-
-    if (!member.isNull()) {
-        return member;
-    } else {
-        return {};
-    }
-}
-
-template<> optional<Error> ValueTraits<AndroidValue>::eachMember(const AndroidValue&, const std::function<optional<Error> (const std::string&, const AndroidValue&)>&) {
-    // TODO
-    mbgl::Log::Warning(mbgl::Event::Android, "eachMember not implemented");
-    return {};
-}
-
-template<> optional<bool> ValueTraits<AndroidValue>::toBool(const AndroidValue& value) {
-    if (value.isBool()) {
-        return value.toBool();
-    } else {
-        return {};
-    }
-}
-
-template<> optional<float> ValueTraits<AndroidValue>::toNumber(const AndroidValue& value) {
-    if (value.isNumber()) {
-        auto num = value.toFloat();
-        return num;
-    } else {
-        return {};
-    }
-}
-
-template<> optional<double> ValueTraits<AndroidValue>::toDouble(const AndroidValue& value) {
-    if (value.isNumber()) {
-        return value.toDouble();
-    } else {
-        return {};
-    }
-}
-
-template<> optional<std::string> ValueTraits<AndroidValue>::toString(const AndroidValue& value) {
-    if (value.isString()) {
-        return value.toString();
-    } else {
-        return {};
-    }
-}
-
-template<> optional<mbgl::Value> ValueTraits<AndroidValue>::toValue(const AndroidValue& 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 {};
-    }
-}
-
-template<> optional<GeoJSON> ValueTraits<AndroidValue>::toGeoJSON(const AndroidValue &value, Error &error) {
-    if(value.isNull() || !value.isString()) {
-        error = { "no json data found" };
-        return {};
-    }
-
-    return parseGeoJSON(value.toString(), error);
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/platform/android/src/style/android_conversion.hpp b/platform/android/src/style/android_conversion.hpp
index 3969553816..bc067fbc53 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>
 
@@ -13,6 +14,101 @@ namespace mbgl {
 namespace style {
 namespace conversion {
 
+template <>
+class ValueTraits<mbgl::android::Value> {
+public:
+    static bool isUndefined(const mbgl::android::Value& value) {
+        return value.isNull();
+    }
+
+    static bool isArray(const mbgl::android::Value& value) {
+        return value.isArray();
+    }
+
+    static bool isObject(const mbgl::android::Value& value) {
+        return value.isObject();
+    }
+
+    static std::size_t arrayLength(const mbgl::android::Value& value) {
+        return value.getLength();;
+    }
+
+    static mbgl::android::Value arrayMember(const mbgl::android::Value& value, std::size_t i) {
+        return value.get(i);
+    }
+
+    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 {};
+        }
+    }
+
+    static optional<Error> eachMember(const mbgl::android::Value&, const std::function<optional<Error> (const std::string&, const mbgl::android::Value&)>&) {
+        // 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 {};
+        }
+    }
+
+    static 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 {};
+        }
+    }
+
+    static optional<std::string> toString(const mbgl::android::Value& value) {
+        if (value.isString()) {
+            return value.toString();
+        } else {
+            return {};
+        }
+    }
+
+    static optional<mbgl::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(const mbgl::android::Value& value, Error& error, Args&&...args) {
     return convert<T>(Value(value), error, std::forward<Args>(args)...);
diff --git a/platform/darwin/src/MGLConversion.h b/platform/darwin/src/MGLConversion.h
index a354c28cd9..f5db1acfe5 100644
--- a/platform/darwin/src/MGLConversion.h
+++ b/platform/darwin/src/MGLConversion.h
@@ -6,7 +6,142 @@ namespace mbgl {
 namespace style {
 namespace conversion {
 
-Value makeValue(const id value);
+class Holder {
+public:
+    Holder(const id v) : value(v) {}
+    const id value;
+};
+
+template <>
+class ValueTraits<Holder> {
+public:
+    static bool isUndefined(const Holder& holder) {
+        const id value = holder.value;
+        return !value || value == [NSNull null];
+    }
+
+    static bool isArray(const Holder& holder) {
+        const id value = holder.value;
+        return [value isKindOfClass:[NSArray class]];
+    }
+
+    static bool isObject(const Holder& holder) {
+        const id value = holder.value;
+        return [value isKindOfClass:[NSDictionary 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;
+    }
+
+    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]};
+    }
+
+    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 {};
+        }
+    }
+
+    static optional<Error> eachMember(const Holder& holder, const std::function<optional<Error> (const std::string&, const Holder&)>& fn) {
+        // Not implemented (unneeded for MGLStyleFunction conversion).
+        NSCAssert(NO, @"eachMember not implemented");
+        return {};
+    }
+
+    static optional<bool> toBool(const Holder& holder) {
+        const id value = holder.value;
+        if (_isBool(value)) {
+            return ((NSNumber *)value).boolValue;
+        } else {
+            return {};
+        }
+    }
+
+    static optional<float> toNumber(const Holder& holder) {
+        const id value = holder.value;
+        if (_isNumber(value)) {
+            return ((NSNumber *)value).floatValue;
+        } else {
+            return {};
+        }
+    }
+
+    static optional<double> toDouble(const Holder& holder) {
+        const id value = holder.value;
+        if (_isNumber(value)) {
+            return ((NSNumber *)value).doubleValue;
+        } 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 {};
+        }
+    }
+
+    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 {};
+        }
+    }
+
+    static optional<GeoJSON> toGeoJSON(const Holder& holder, Error& error) {
+        error = { "toGeoJSON not implemented" };
+        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));
+    }
+
+    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 Value makeValue(const id value) {
+    return {Holder(value)};
+}
 
 } // namespace conversion
 } // namespace style
diff --git a/platform/darwin/src/MGLConversion.mm b/platform/darwin/src/MGLConversion.mm
deleted file mode 100644
index 890a96c34d..0000000000
--- a/platform/darwin/src/MGLConversion.mm
+++ /dev/null
@@ -1,149 +0,0 @@
-#import <Foundation/Foundation.h>
-
-#include "MGLConversion.h"
-
-NS_ASSUME_NONNULL_BEGIN
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-class Holder {
-public:
-    Holder(const id v) : value(v) {}
-    const id value;
-};
-
-template<> bool ValueTraits<Holder>::isUndefined(const Holder& holder) {
-    const id value = holder.value;
-    return !value || value == [NSNull null];
-}
-
-template<> bool ValueTraits<Holder>::isArray(const Holder& holder) {
-    const id value = holder.value;
-    return [value isKindOfClass:[NSArray class]];
-}
-
-template<> bool ValueTraits<Holder>::isObject(const Holder& holder) {
-    const id value = holder.value;
-    return [value isKindOfClass:[NSDictionary class]];
-}
-
-template<> std::size_t ValueTraits<Holder>::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;
-}
-
-template<> Holder ValueTraits<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]};
-}
-
-template<> optional<Holder> ValueTraits<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 {};
-    }
-}
-
-template<> optional<Error> ValueTraits<Holder>::eachMember(const Holder& holder, const std::function<optional<Error> (const std::string&, const Holder&)>& fn) {
-    // Not implemented (unneeded for MGLStyleFunction conversion).
-    NSCAssert(NO, @"eachMember not implemented");
-    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]];
-}
-
-template<> optional<bool> ValueTraits<Holder>::toBool(const Holder& holder) {
-    const id value = holder.value;
-    if (_isBool(value)) {
-        return ((NSNumber *)value).boolValue;
-    } else {
-        return {};
-    }
-}
-
-template<> optional<float> ValueTraits<Holder>::toNumber(const Holder& holder) {
-    const id value = holder.value;
-    if (_isNumber(value)) {
-        return ((NSNumber *)value).floatValue;
-    } else {
-        return {};
-    }
-}
-
-template<> optional<double> ValueTraits<Holder>::toDouble(const Holder& holder) {
-    const id value = holder.value;
-    if (_isNumber(value)) {
-        return ((NSNumber *)value).doubleValue;
-    } else {
-        return {};
-    }
-}
-
-template<> optional<std::string> ValueTraits<Holder>::toString(const Holder& holder) {
-    const id value = holder.value;
-    if (_isString(value)) {
-        return std::string(static_cast<const char *>([value UTF8String]));
-    } else {
-        return {};
-    }
-}
-
-template<> optional<mbgl::Value> ValueTraits<Holder>::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 {};
-    }
-}
-
-template<> optional<GeoJSON> ValueTraits<Holder>::toGeoJSON(const Holder& holder, Error& error) {
-    error = { "toGeoJSON not implemented" };
-    return {};
-}
-
-Value makeValue(const id value) {
-    return {Holder(value)};
-}
-
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
-
-NS_ASSUME_NONNULL_END
-
diff --git a/platform/ios/ios.xcodeproj/project.pbxproj b/platform/ios/ios.xcodeproj/project.pbxproj
index 63fc76b2df..a3ccc9337b 100644
--- a/platform/ios/ios.xcodeproj/project.pbxproj
+++ b/platform/ios/ios.xcodeproj/project.pbxproj
@@ -14,8 +14,6 @@
 		071BBB071EE77631001FB02A /* MGLImageSourceTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 071BBB051EE7761A001FB02A /* MGLImageSourceTests.m */; };
 		1753ED421E53CE6F00A9FD90 /* MGLConversion.h in Headers */ = {isa = PBXBuildFile; fileRef = 1753ED411E53CE6F00A9FD90 /* MGLConversion.h */; };
 		1753ED431E53CE6F00A9FD90 /* MGLConversion.h in Headers */ = {isa = PBXBuildFile; fileRef = 1753ED411E53CE6F00A9FD90 /* MGLConversion.h */; };
-		17DBEF831F95066000E60A6B /* MGLConversion.mm in Sources */ = {isa = PBXBuildFile; fileRef = 17DBEF821F95066000E60A6B /* MGLConversion.mm */; };
-		17DBEF841F95066000E60A6B /* MGLConversion.mm in Sources */ = {isa = PBXBuildFile; fileRef = 17DBEF821F95066000E60A6B /* MGLConversion.mm */; };
 		1F06668A1EC64F8E001C16D7 /* MGLLight.h in Headers */ = {isa = PBXBuildFile; fileRef = 1F0666881EC64F8E001C16D7 /* MGLLight.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		1F06668D1EC64F8E001C16D7 /* MGLLight.mm in Sources */ = {isa = PBXBuildFile; fileRef = 1F0666891EC64F8E001C16D7 /* MGLLight.mm */; };
 		1F7454921ECBB42C00021D39 /* MGLLight.mm in Sources */ = {isa = PBXBuildFile; fileRef = 1F0666891EC64F8E001C16D7 /* MGLLight.mm */; };
@@ -574,7 +572,6 @@
 		071BBAFD1EE75CD4001FB02A /* MGLImageSource.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLImageSource.mm; sourceTree = "<group>"; };
 		071BBB051EE7761A001FB02A /* MGLImageSourceTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = MGLImageSourceTests.m; path = ../../darwin/test/MGLImageSourceTests.m; sourceTree = "<group>"; };
 		1753ED411E53CE6F00A9FD90 /* MGLConversion.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLConversion.h; sourceTree = "<group>"; };
-		17DBEF821F95066000E60A6B /* MGLConversion.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLConversion.mm; sourceTree = "<group>"; };
 		1F0666881EC64F8E001C16D7 /* MGLLight.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLLight.h; sourceTree = "<group>"; };
 		1F0666891EC64F8E001C16D7 /* MGLLight.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLLight.mm; sourceTree = "<group>"; };
 		1F7454941ECD450D00021D39 /* MGLLight_Private.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLLight_Private.h; sourceTree = "<group>"; };
@@ -1097,7 +1094,6 @@
 		35599DA21D4682B60048254D /* Styling */ = {
 			isa = PBXGroup;
 			children = (
-				17DBEF821F95066000E60A6B /* MGLConversion.mm */,
 				1753ED411E53CE6F00A9FD90 /* MGLConversion.h */,
 				35599DB81D46AD7F0048254D /* Categories */,
 				353933F01D3FB6BA003F57D7 /* Layers */,
@@ -2328,7 +2324,6 @@
 				DA8848501CBAFB9800AB86E3 /* MGLAnnotationImage.m in Sources */,
 				DA8848281CBAFA6200AB86E3 /* MGLShape.mm in Sources */,
 				DA35A2B31CCA141D00E826B2 /* MGLCompassDirectionFormatter.m in Sources */,
-				17DBEF831F95066000E60A6B /* MGLConversion.mm in Sources */,
 				DD0902A91DB1929D00C5BDCE /* MGLNetworkConfiguration.m in Sources */,
 				35D13AB91D3D15E300AFB4E0 /* MGLStyleLayer.mm in Sources */,
 				DA35A2CB1CCAAAD200E826B2 /* NSValue+MGLAdditions.m in Sources */,
@@ -2416,7 +2411,6 @@
 				DAA4E41F1CBB730400178DFB /* MGLMultiPoint.mm in Sources */,
 				DD0902AA1DB1929D00C5BDCE /* MGLNetworkConfiguration.m in Sources */,
 				DA35A2B41CCA141D00E826B2 /* MGLCompassDirectionFormatter.m in Sources */,
-				17DBEF841F95066000E60A6B /* MGLConversion.mm in Sources */,
 				35D13ABA1D3D15E300AFB4E0 /* MGLStyleLayer.mm in Sources */,
 				071BBAFF1EE7613E001FB02A /* MGLImageSource.mm in Sources */,
 				DA35A2CC1CCAAAD200E826B2 /* NSValue+MGLAdditions.m in Sources */,
diff --git a/platform/macos/macos.xcodeproj/project.pbxproj b/platform/macos/macos.xcodeproj/project.pbxproj
index 6f99382b02..34f8860686 100644
--- a/platform/macos/macos.xcodeproj/project.pbxproj
+++ b/platform/macos/macos.xcodeproj/project.pbxproj
@@ -73,7 +73,6 @@
 		40B77E451DB11BC9003DA2FE /* NSArray+MGLAdditions.h in Headers */ = {isa = PBXBuildFile; fileRef = 40B77E431DB11BB0003DA2FE /* NSArray+MGLAdditions.h */; };
 		40B77E461DB11BCD003DA2FE /* NSArray+MGLAdditions.mm in Sources */ = {isa = PBXBuildFile; fileRef = 40B77E421DB11BB0003DA2FE /* NSArray+MGLAdditions.mm */; };
 		40E1601D1DF217D6005EA6D9 /* MGLStyleLayerTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 40E1601B1DF216E6005EA6D9 /* MGLStyleLayerTests.m */; };
-		5241C2BE1F7AFFAF00DDB20E /* MGLConversion.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5241C2BD1F7AFFAF00DDB20E /* MGLConversion.mm */; };
 		52B5D17F1E5E26DF00BBCB48 /* libmbgl-loop-darwin.a in Frameworks */ = {isa = PBXBuildFile; fileRef = 5548BE7B1D0ACBBD005DDE81 /* libmbgl-loop-darwin.a */; };
 		52B5D1801E5E26DF00BBCB48 /* libmbgl-loop-darwin.a in Frameworks */ = {isa = PBXBuildFile; fileRef = 5548BE7B1D0ACBBD005DDE81 /* libmbgl-loop-darwin.a */; };
 		5548BE781D09E718005DDE81 /* libmbgl-core.a in Frameworks */ = {isa = PBXBuildFile; fileRef = DAE6C3451CC31D1200DB3429 /* libmbgl-core.a */; };
@@ -350,7 +349,6 @@
 		40B77E431DB11BB0003DA2FE /* NSArray+MGLAdditions.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSArray+MGLAdditions.h"; sourceTree = "<group>"; };
 		40E1601A1DF216E6005EA6D9 /* MGLStyleLayerTests.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLStyleLayerTests.h; sourceTree = "<group>"; };
 		40E1601B1DF216E6005EA6D9 /* MGLStyleLayerTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MGLStyleLayerTests.m; sourceTree = "<group>"; };
-		5241C2BD1F7AFFAF00DDB20E /* MGLConversion.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLConversion.mm; sourceTree = "<group>"; };
 		52BECB091CC5A26F009CD791 /* SystemConfiguration.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SystemConfiguration.framework; path = System/Library/Frameworks/SystemConfiguration.framework; sourceTree = SDKROOT; };
 		5548BE7B1D0ACBBD005DDE81 /* libmbgl-loop-darwin.a */ = {isa = PBXFileReference; lastKnownFileType = archive.ar; name = "libmbgl-loop-darwin.a"; path = "cmake/Debug/libmbgl-loop-darwin.a"; sourceTree = "<group>"; };
 		556660C51E1BEA0100E2C41B /* MGLFoundation.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = MGLFoundation.h; sourceTree = "<group>"; };
@@ -700,7 +698,6 @@
 			isa = PBXGroup;
 			children = (
 				1753ED3F1E53CE5200A9FD90 /* MGLConversion.h */,
-				5241C2BD1F7AFFAF00DDB20E /* MGLConversion.mm */,
 				352742791D4C235C00A1ECE6 /* Categories */,
 				35136D471D42295400C20EFD /* Layers */,
 				3527427E1D4C242B00A1ECE6 /* Sources */,
@@ -730,14 +727,6 @@
 			name = "Test Helpers";
 			sourceTree = "<group>";
 		};
-		5241C2BA1F7AF16100DDB20E /* Recovered References */ = {
-			isa = PBXGroup;
-			children = (
-				30E578141DAA7D920050F07E /* NSImage+MGLAdditions.h */,
-			);
-			name = "Recovered References";
-			sourceTree = "<group>";
-		};
 		DA839E891CC2E3400062CAFB = {
 			isa = PBXGroup;
 			children = (
@@ -747,7 +736,6 @@
 				DAE6C31E1CC308BC00DB3429 /* Frameworks */,
 				DAE6C3C41CC31F7800DB3429 /* Configuration */,
 				DA839E931CC2E3400062CAFB /* Products */,
-				5241C2BA1F7AF16100DDB20E /* Recovered References */,
 			);
 			sourceTree = "<group>";
 		};
@@ -1445,7 +1433,6 @@
 				1FCDF1431F2A4F3600A46694 /* MGLVectorSource+MGLAdditions.m in Sources */,
 				DD0902B21DB1AC6400C5BDCE /* MGLNetworkConfiguration.m in Sources */,
 				1F7454A51ECFB00300021D39 /* MGLLight.mm in Sources */,
-				5241C2BE1F7AFFAF00DDB20E /* MGLConversion.mm in Sources */,
 				DAE6C3B11CC31EF300DB3429 /* MGLAnnotationImage.m in Sources */,
 				3508EC651D749D39009B0EE4 /* NSExpression+MGLAdditions.mm in Sources */,
 				DACC22151CF3D3E200D220D9 /* MGLFeature.mm in Sources */,
diff --git a/platform/node/src/node_conversion.cpp b/platform/node/src/node_conversion.cpp
deleted file mode 100644
index ed082615d0..0000000000
--- a/platform/node/src/node_conversion.cpp
+++ /dev/null
@@ -1,137 +0,0 @@
-#include "node_conversion.hpp"
-#include <mbgl/style/conversion/geojson.hpp>
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template<> bool ValueTraits<v8::Local<v8::Value>>::isUndefined(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    return value->IsUndefined() || value->IsNull();
-}
-
-template<> bool ValueTraits<v8::Local<v8::Value>>::isArray(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    return value->IsArray();
-}
-
-template<> std::size_t ValueTraits<v8::Local<v8::Value>>::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();
-}
-
-template<> v8::Local<v8::Value> ValueTraits<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());
-}
-
-template<> bool ValueTraits<v8::Local<v8::Value>>::isObject(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    return value->IsObject() && !value->IsArray();
-}
-
-template<> optional<v8::Local<v8::Value>> ValueTraits<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())};
-}
-
-template<> optional<Error> ValueTraits<v8::Local<v8::Value>>::eachMember(const v8::Local<v8::Value>& value, const std::function<optional<Error> (const std::string&, const v8::Local<v8::Value>&)>& 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;
-        }
-    }
-    return {};
-}
-
-template<> optional<bool> ValueTraits<v8::Local<v8::Value>>::toBool(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    if (!value->IsBoolean()) {
-        return {};
-    }
-    return value->BooleanValue();
-}
-
-template<> optional<float> ValueTraits<v8::Local<v8::Value>>::toNumber(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    if (!value->IsNumber()) {
-        return {};
-    }
-    return value->NumberValue();
-}
-
-template<> optional<double> ValueTraits<v8::Local<v8::Value>>::toDouble(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    if (!value->IsNumber()) {
-        return {};
-    }
-    return value->NumberValue();
-}
-
-template<> optional<std::string> ValueTraits<v8::Local<v8::Value>>::toString(const v8::Local<v8::Value>& value) {
-    Nan::HandleScope scope;
-    
-    if (!value->IsString()) {
-        return {};
-    }
-    return std::string(*Nan::Utf8String(value));
-}
-
-template<> optional<mbgl::Value> ValueTraits<v8::Local<v8::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 {};
-    }
-}
-
-template<> optional<GeoJSON> ValueTraits<v8::Local<v8::Value>>::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 {};
-    }
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/platform/node/src/node_conversion.hpp b/platform/node/src/node_conversion.hpp
index 7f0a7ed39e..7db5b23642 100644
--- a/platform/node/src/node_conversion.hpp
+++ b/platform/node/src/node_conversion.hpp
@@ -9,17 +9,137 @@
 #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 {
 
+template <>
+class ValueTraits<v8::Local<v8::Value>> {
+public:
+    static bool isUndefined(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsUndefined() || value->IsNull();
+    }
+
+    static bool isArray(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsArray();
+    }
+
+    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();
+    }
+
+    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());
+    }
+
+    static bool isObject(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        return value->IsObject() && !value->IsArray();
+    }
+
+    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())};
+    }
+
+    static optional<Error> eachMember(const v8::Local<v8::Value>& value, const std::function<optional<Error> (const std::string&, const v8::Local<v8::Value>&)>& 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;
+            }
+        }
+        return {};
+    }
+
+    static optional<bool> toBool(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsBoolean()) {
+            return {};
+        }
+        return value->BooleanValue();
+    }
+
+    static optional<float> toNumber(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->NumberValue();
+    }
+
+    static optional<double> toDouble(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->NumberValue();
+    }
+
+    static optional<std::string> toString(const v8::Local<v8::Value>& value) {
+        Nan::HandleScope scope;
+        if (!value->IsString()) {
+            return {};
+        }
+        return std::string(*Nan::Utf8String(value));
+    }
+
+    static optional<mbgl::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 {};
+        }
+    }
+
+    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>(Value(value), error, std::forward<Args>(args)...);
 }
 
-
 } // namespace conversion
 } // namespace style
 } // namespace mbgl
diff --git a/platform/qt/qt.cmake b/platform/qt/qt.cmake
index 918e6b93cd..a7862c3936 100644
--- a/platform/qt/qt.cmake
+++ b/platform/qt/qt.cmake
@@ -60,7 +60,6 @@ set(MBGL_QT_FILESOURCE_FILES
 add_library(qmapboxgl SHARED
     platform/qt/include/qmapbox.hpp
     platform/qt/include/qmapboxgl.hpp
-    platform/qt/src/qt_conversion.cpp
     platform/qt/src/qt_conversion.hpp
     platform/qt/src/qt_geojson.cpp
     platform/qt/src/qt_geojson.hpp
diff --git a/platform/qt/src/qt_conversion.cpp b/platform/qt/src/qt_conversion.cpp
deleted file mode 100644
index 35a6ef4fc9..0000000000
--- a/platform/qt/src/qt_conversion.cpp
+++ /dev/null
@@ -1,133 +0,0 @@
-#include <mbgl/util/feature.hpp>
-#include <mbgl/style/conversion/geojson.hpp>
-#include <QColor>
-#include <QMapbox>
-#include "qt_geojson.hpp"
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template<> bool ValueTraits<QVariant>::isUndefined(const QVariant& value) {
-    return value.isNull() || !value.isValid();
-}
-
-template<> bool ValueTraits<QVariant>::isArray(const QVariant& value) {
-    return value.canConvert(QVariant::List);
-}
-
-template<> std::size_t ValueTraits<QVariant>::arrayLength(const QVariant& value) {
-    return value.toList().size();
-}
-
-template<> QVariant ValueTraits<QVariant>::arrayMember(const QVariant& value, std::size_t i) {
-    return value.toList()[i];
-}
-
-template<> bool ValueTraits<QVariant>::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
-}
-
-template<> optional<QVariant> ValueTraits<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 {};
-    }
-}
-
-using EachMemberFn = std::function<optional<Error>(const std::string&, const QVariant&)>;
-
-template<> optional<Error> ValueTraits<QVariant>::eachMember(const QVariant& value, const EachMemberFn& fn) {
-    auto map = value.toMap();
-    auto iter = map.constBegin();
-
-    while (iter != map.constEnd()) {
-        optional<Error> result = fn(iter.key().toStdString(), iter.value());
-        if (result) {
-            return result;
-        }
-
-        ++iter;
-    }
-
-    return {};
-}
-
-template<> optional<bool> ValueTraits<QVariant>::toBool(const QVariant& value) {
-    if (value.type() == QVariant::Bool) {
-        return value.toBool();
-    } else {
-        return {};
-    }
-}
-
-template<> optional<float> ValueTraits<QVariant>::toNumber(const QVariant& value) {
-    if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
-        return value.toFloat();
-    } else {
-        return {};
-    }
-}
-template<> optional<double> ValueTraits<QVariant>::toDouble(const QVariant& value) {
-    if (value.type() == QVariant::Int || value.type() == QVariant::Double) {
-        return value.toDouble();
-    } else {
-        return {};
-    }
-}
-
-template<> optional<std::string> ValueTraits<QVariant>::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 {};
-    }
-}
-
-template<> optional<mbgl::Value> ValueTraits<QVariant>::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 {};
-    }
-}
-
-template <> optional<GeoJSON> ValueTraits<QVariant>::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);
-}
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/platform/qt/src/qt_conversion.hpp b/platform/qt/src/qt_conversion.hpp
index bd830f8432..3f58147ca2 100644
--- a/platform/qt/src/qt_conversion.hpp
+++ b/platform/qt/src/qt_conversion.hpp
@@ -1,13 +1,143 @@
 #pragma once
 
 #include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/geojson.hpp>
 #include <mbgl/util/optional.hpp>
+
 #include <QVariant>
+#include <QColor>
+#include <QMapbox>
+#include "qt_geojson.hpp"
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
+template <>
+class ValueTraits<QVariant> {
+public:
+    static bool isUndefined(const QVariant& value) {
+        return value.isNull() || !value.isValid();
+    }
+
+    static bool isArray(const QVariant& value) {
+        return value.canConvert(QVariant::List);
+    }
+
+    static std::size_t arrayLength(const QVariant& value) {
+        return value.toList().size();
+    }
+
+    static QVariant arrayMember(const QVariant& value, std::size_t i) {
+        return value.toList()[i];
+    }
+
+    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
+    }
+
+    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 {};
+        }
+    }
+
+    using EachMemberFn = std::function<optional<Error>(const std::string&, const QVariant&)>;
+
+    static optional<Error> eachMember(const QVariant& value, const EachMemberFn& fn) {
+        auto map = value.toMap();
+        auto iter = map.constBegin();
+
+        while (iter != map.constEnd()) {
+            optional<Error> result = fn(iter.key().toStdString(), iter.value());
+            if (result) {
+                return result;
+            }
+
+            ++iter;
+        }
+
+        return {};
+    }
+
+    static 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 {};
+        }
+    }
+
+    static 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 {};
+        }
+    }
+
+    static optional<mbgl::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>(Value(value), error, std::forward<Args>(args)...);
diff --git a/src/mbgl/style/rapidjson_conversion.cpp b/src/mbgl/style/rapidjson_conversion.cpp
deleted file mode 100644
index a6162f1b77..0000000000
--- a/src/mbgl/style/rapidjson_conversion.cpp
+++ /dev/null
@@ -1,112 +0,0 @@
-#include <mbgl/style/rapidjson_conversion.hpp>
-#include <mapbox/geojson.hpp>
-#include <mapbox/geojson/rapidjson.hpp>
-
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-template<> bool ValueTraits<const JSValue*>::isUndefined(const JSValue* const& value) {
-    return value->IsNull();
-}
-
-template<> bool ValueTraits<const JSValue*>::isArray(const JSValue* const& value) {
-    return value->IsArray();
-}
-
-template<> std::size_t ValueTraits<const JSValue*>::arrayLength(const JSValue* const& value) {
-    return value->Size();
-}
-
-template<> const JSValue* ValueTraits<const JSValue*>::arrayMember(const JSValue* const& value, std::size_t i) {
-    return &(*value)[rapidjson::SizeType(i)];
-}
-
-template<> bool ValueTraits<const JSValue*>::isObject(const JSValue* const& value) {
-    return value->IsObject();
-}
-
-template<> optional<const JSValue*> ValueTraits<const JSValue*>::objectMember(const JSValue* const& value, const char * name) {
-    if (!value->HasMember(name)) {
-        return optional<const JSValue*>();
-    }
-    const JSValue* const& member = &(*value)[name];
-    return {member};
-}
-
-template<> optional<Error> ValueTraits<const JSValue*>::eachMember(const JSValue* const& value, const std::function<optional<Error> (const std::string&, const JSValue* const&)>& fn) {
-    assert(value->IsObject());
-    for (const auto& property : value->GetObject()) {
-        optional<Error> result =
-            fn({ property.name.GetString(), property.name.GetStringLength() }, &property.value);
-        if (result) {
-            return result;
-        }
-    }
-    return {};
-}
-
-template<> optional<bool> ValueTraits<const JSValue*>::toBool(const JSValue* const& value) {
-    if (!value->IsBool()) {
-        return {};
-    }
-    return value->GetBool();
-}
-
-template<> optional<float> ValueTraits<const JSValue*>::toNumber(const JSValue* const& value) {
-    if (!value->IsNumber()) {
-        return {};
-    }
-    return value->GetDouble();
-}
-
-template<> optional<double> ValueTraits<const JSValue*>::toDouble(const JSValue* const& value) {
-    if (!value->IsNumber()) {
-        return {};
-    }
-    return value->GetDouble();
-}
-
-template<> optional<std::string> ValueTraits<const JSValue*>::toString(const JSValue* const& value) {
-    if (!value->IsString()) {
-        return {};
-    }
-    return {{ value->GetString(), value->GetStringLength() }};
-}
-
-template<> optional<mbgl::Value> ValueTraits<const JSValue*>::toValue(const JSValue* const& value) {
-    switch (value->GetType()) {
-        case rapidjson::kNullType:
-        case rapidjson::kFalseType:
-            return { false };
-
-        case rapidjson::kTrueType:
-            return { true };
-
-        case rapidjson::kStringType:
-            return { std::string { value->GetString(), value->GetStringLength() } };
-
-        case rapidjson::kNumberType:
-            if (value->IsUint64()) return { value->GetUint64() };
-            if (value->IsInt64()) return { value->GetInt64() };
-            return { value->GetDouble() };
-
-        default:
-            return {};
-    }
-}
-
-template<> optional<GeoJSON> ValueTraits<const JSValue*>::toGeoJSON(const JSValue* const& value, Error& error) {
-    try {
-        return mapbox::geojson::convert(*value);
-    } catch (const std::exception& ex) {
-        error = { ex.what() };
-        return {};
-    }
-}
-
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/src/mbgl/style/rapidjson_conversion.hpp b/src/mbgl/style/rapidjson_conversion.hpp
index 082fd1c064..ae3ead24b0 100644
--- a/src/mbgl/style/rapidjson_conversion.hpp
+++ b/src/mbgl/style/rapidjson_conversion.hpp
@@ -3,10 +3,116 @@
 #include <mbgl/util/rapidjson.hpp>
 #include <mbgl/style/conversion.hpp>
 
+#include <mapbox/geojson.hpp>
+#include <mapbox/geojson/rapidjson.hpp>
+
 namespace mbgl {
 namespace style {
 namespace conversion {
 
+template <>
+class ValueTraits<const JSValue*> {
+public:
+    static bool isUndefined(const JSValue* value) {
+        return value->IsNull();
+    }
+
+    static bool isArray(const JSValue* value) {
+        return value->IsArray();
+    }
+
+    static std::size_t arrayLength(const JSValue* value) {
+        return value->Size();
+    }
+
+    static const JSValue* arrayMember(const JSValue* value, std::size_t i) {
+        return &(*value)[rapidjson::SizeType(i)];
+    }
+
+    static bool isObject(const JSValue* value) {
+        return value->IsObject();
+    }
+
+    static optional<const JSValue*> objectMember(const JSValue* value, const char * name) {
+        if (!value->HasMember(name)) {
+            return optional<const JSValue*>();
+        }
+        const JSValue* const& member = &(*value)[name];
+        return {member};
+    }
+
+    static optional<Error> eachMember(const JSValue* value, const std::function<optional<Error> (const std::string&, const JSValue* const&)>& fn) {
+        assert(value->IsObject());
+        for (const auto& property : value->GetObject()) {
+            optional<Error> result =
+                fn({ property.name.GetString(), property.name.GetStringLength() }, &property.value);
+            if (result) {
+                return result;
+            }
+        }
+        return {};
+    }
+
+    static optional<bool> toBool(const JSValue* value) {
+        if (!value->IsBool()) {
+            return {};
+        }
+        return value->GetBool();
+    }
+
+    static optional<float> toNumber(const JSValue* value) {
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->GetDouble();
+    }
+
+    static optional<double> toDouble(const JSValue* value) {
+        if (!value->IsNumber()) {
+            return {};
+        }
+        return value->GetDouble();
+    }
+
+    static optional<std::string> toString(const JSValue* value) {
+        if (!value->IsString()) {
+            return {};
+        }
+        return {{ value->GetString(), value->GetStringLength() }};
+    }
+
+    static optional<mbgl::Value> toValue(const JSValue* value) {
+        switch (value->GetType()) {
+            case rapidjson::kNullType:
+            case rapidjson::kFalseType:
+                return { false };
+
+            case rapidjson::kTrueType:
+                return { true };
+
+            case rapidjson::kStringType:
+                return { std::string { value->GetString(), value->GetStringLength() } };
+
+            case rapidjson::kNumberType:
+                if (value->IsUint64()) return { value->GetUint64() };
+                if (value->IsInt64()) return { value->GetInt64() };
+                return { value->GetDouble() };
+
+            default:
+                return {};
+        }
+    }
+
+    static optional<GeoJSON> toGeoJSON(const JSValue* value, Error& error) {
+        try {
+            return mapbox::geojson::convert(*value);
+        } catch (const std::exception& ex) {
+            error = { ex.what() };
+            return {};
+        }
+    }
+};
+
 template <class T, class...Args>
 optional<T> convert(const JSValue& value, Error& error, Args&&...args) {
     return convert<T>(Value(&value), error, std::forward<Args>(args)...);