[core] Simplify property parsing

This is a followup to #4811. Now that use of Function is consistent, we can have a single separate parseProperty template function that delegates to a parseConstant template function.

4 files changed, 115 insertions, 176 deletions

diff --git a/src/mbgl/style/layout_property.hpp b/src/mbgl/style/layout_property.hpp
index 894fc44467..dd3c032152 100644
--- a/src/mbgl/style/layout_property.hpp
+++ b/src/mbgl/style/layout_property.hpp
@@ -17,7 +17,7 @@ public:
 
     void parse(const char * name, const JSValue& layout) {
         if (layout.HasMember(name)) {
-            parsedValue = parseProperty<Function<T>>(name, layout[name]);
+            parsedValue = parseProperty<T>(name, layout[name]);
         }
     }
 
diff --git a/src/mbgl/style/paint_property.hpp b/src/mbgl/style/paint_property.hpp
index 124b0a7c0a..3c2b4ba7d7 100644
--- a/src/mbgl/style/paint_property.hpp
+++ b/src/mbgl/style/paint_property.hpp
@@ -51,14 +51,14 @@ public:
             ClassID classID = isClass ? ClassDictionary::Get().lookup(paintName.substr(6)) : ClassID::Default;
 
             if (it->value.HasMember(name)) {
-                auto v = parseProperty<Fn>(name, it->value[name]);
+                auto v = parseProperty<T>(name, it->value[name]);
                 if (v) {
                     values.emplace(classID, *v);
                 }
             }
 
             if (it->value.HasMember(transitionName.c_str())) {
-                auto v = parseProperty<PropertyTransition>(name, it->value[transitionName.c_str()]);
+                auto v = parsePropertyTransition(name, it->value[transitionName.c_str()]);
                 if (v) {
                     transitions.emplace(classID, *v);
                 }
diff --git a/src/mbgl/style/property_parsing.cpp b/src/mbgl/style/property_parsing.cpp
index 84589ea414..7994f245e8 100644
--- a/src/mbgl/style/property_parsing.cpp
+++ b/src/mbgl/style/property_parsing.cpp
@@ -1,17 +1,11 @@
 #include <mbgl/style/property_parsing.hpp>
-#include <mbgl/style/property_transition.hpp>
-#include <mbgl/style/function.hpp>
-
-#include <mbgl/platform/log.hpp>
 
 #include <csscolorparser/csscolorparser.hpp>
 
-#include <vector>
-
 namespace mbgl {
 
 template <>
-optional<bool> parseProperty(const char* name, const JSValue& value) {
+optional<bool> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsBool()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a boolean", name);
         return {};
@@ -21,7 +15,7 @@ optional<bool> parseProperty(const char* name, const JSValue& value) {
 }
 
 template <>
-optional<float> parseProperty(const char* name, const JSValue& value) {
+optional<float> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsNumber()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a number, or a number function", name);
         return {};
@@ -31,7 +25,7 @@ optional<float> parseProperty(const char* name, const JSValue& value) {
 }
 
 template <>
-optional<std::string> parseProperty(const char* name, const JSValue& value) {
+optional<std::string> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -41,7 +35,7 @@ optional<std::string> parseProperty(const char* name, const JSValue& value) {
 }
 
 template <>
-optional<Color> parseProperty(const char* name, const JSValue& value) {
+optional<Color> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -64,7 +58,7 @@ MBGL_DEFINE_ENUM_CLASS(TranslateAnchorTypeClass, TranslateAnchorType, {
 });
 
 template <>
-optional<TranslateAnchorType> parseProperty(const char* name, const JSValue& value) {
+optional<TranslateAnchorType> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -79,7 +73,7 @@ MBGL_DEFINE_ENUM_CLASS(RotateAnchorTypeClass, RotateAnchorType, {
 });
 
 template <>
-optional<RotateAnchorType> parseProperty<RotateAnchorType>(const char* name, const JSValue& value) {
+optional<RotateAnchorType> parseConstant<RotateAnchorType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -95,7 +89,7 @@ MBGL_DEFINE_ENUM_CLASS(LineCapTypeClass, LineCapType, {
 });
 
 template <>
-optional<LineCapType> parseProperty<LineCapType>(const char* name, const JSValue& value) {
+optional<LineCapType> parseConstant<LineCapType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -113,7 +107,7 @@ MBGL_DEFINE_ENUM_CLASS(LineJoinTypeClass, LineJoinType, {
 });
 
 template <>
-optional<LineJoinType> parseProperty<LineJoinType>(const char* name, const JSValue& value) {
+optional<LineJoinType> parseConstant<LineJoinType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -128,7 +122,7 @@ MBGL_DEFINE_ENUM_CLASS(SymbolPlacementTypeClass, SymbolPlacementType, {
 });
 
 template <>
-optional<SymbolPlacementType> parseProperty<SymbolPlacementType>(const char* name, const JSValue& value) {
+optional<SymbolPlacementType> parseConstant<SymbolPlacementType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -150,7 +144,7 @@ MBGL_DEFINE_ENUM_CLASS(TextAnchorTypeClass, TextAnchorType, {
 });
 
 template <>
-optional<TextAnchorType> parseProperty<TextAnchorType>(const char* name, const JSValue& value) {
+optional<TextAnchorType> parseConstant<TextAnchorType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -166,7 +160,7 @@ MBGL_DEFINE_ENUM_CLASS(TextJustifyTypeClass, TextJustifyType, {
 });
 
 template <>
-optional<TextJustifyType> parseProperty<TextJustifyType>(const char* name, const JSValue& value) {
+optional<TextJustifyType> parseConstant<TextJustifyType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -182,7 +176,7 @@ MBGL_DEFINE_ENUM_CLASS(TextTransformTypeClass, TextTransformType, {
 });
 
 template <>
-optional<TextTransformType> parseProperty<TextTransformType>(const char* name, const JSValue& value) {
+optional<TextTransformType> parseConstant<TextTransformType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -197,7 +191,7 @@ MBGL_DEFINE_ENUM_CLASS(RotationAlignmentTypeClass, RotationAlignmentType, {
 });
 
 template <>
-optional<RotationAlignmentType> parseProperty<RotationAlignmentType>(const char* name, const JSValue& value) {
+optional<RotationAlignmentType> parseConstant<RotationAlignmentType>(const char* name, const JSValue& value) {
     if (!value.IsString()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be a string", name);
         return {};
@@ -207,7 +201,7 @@ optional<RotationAlignmentType> parseProperty<RotationAlignmentType>(const char*
 }
 
 template <>
-optional<std::array<float, 2>> parseProperty(const char* name, const JSValue& value) {
+optional<std::array<float, 2>> parseConstant(const char* name, const JSValue& value) {
     if (value.IsArray() && value.Size() == 2 &&
             value[rapidjson::SizeType(0)].IsNumber() &&
             value[rapidjson::SizeType(1)].IsNumber()) {
@@ -222,7 +216,7 @@ optional<std::array<float, 2>> parseProperty(const char* name, const JSValue& va
 }
 
 template <>
-optional<std::vector<float>> parseProperty(const char* name, const JSValue& value) {
+optional<std::vector<float>> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsArray()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be an array of numbers", name);
         return {};
@@ -245,7 +239,7 @@ optional<std::vector<float>> parseProperty(const char* name, const JSValue& valu
 }
 
 template <>
-optional<std::vector<std::string>> parseProperty(const char* name, const JSValue& value) {
+optional<std::vector<std::string>> parseConstant(const char* name, const JSValue& value) {
     if (!value.IsArray()) {
         Log::Warning(Event::ParseStyle, "value of '%s' must be an array of strings", name);
         return {};
@@ -267,8 +261,7 @@ optional<std::vector<std::string>> parseProperty(const char* name, const JSValue
     return result;
 }
 
-template <>
-optional<PropertyTransition> parseProperty(const char *, const JSValue& value) {
+optional<PropertyTransition> parsePropertyTransition(const char *, const JSValue& value) {
     PropertyTransition transition;
     if (value.IsObject()) {
         bool parsed = false;
@@ -287,146 +280,4 @@ optional<PropertyTransition> parseProperty(const char *, const JSValue& value) {
     return transition;
 }
 
-// --- Function ---
-
-template <typename T>
-optional<std::vector<std::pair<float, T>>> parseStops(const char* name, const JSValue& value) {
-    if (!value.IsArray()) {
-        Log::Warning(Event::ParseStyle, "stops function must specify a stops array");
-        return {};
-    }
-
-    std::vector<std::pair<float, T>> stops;
-
-    for (rapidjson::SizeType i = 0; i < value.Size(); ++i) {
-        const JSValue& stop = value[i];
-
-        if (!stop.IsArray()) {
-            Log::Warning(Event::ParseStyle, "function argument must be a numeric value");
-            return {};
-        }
-
-        if (stop.Size() != 2) {
-            Log::Warning(Event::ParseStyle, "stop must have zoom level and value specification");
-            return {};
-        }
-
-        const JSValue& z = stop[rapidjson::SizeType(0)];
-        if (!z.IsNumber()) {
-            Log::Warning(Event::ParseStyle, "zoom level in stop must be a number");
-            return {};
-        }
-
-        optional<T> v = parseProperty<T>(name, stop[rapidjson::SizeType(1)]);
-        if (!v) {
-            return {};
-        }
-
-        stops.emplace_back(z.GetDouble(), *v);
-    }
-
-    return stops;
-}
-
-template <typename T>
-optional<Function<T>> parseFunction(const char* name, const JSValue& value) {
-    if (!value.IsObject()) {
-        auto constant = parseProperty<T>(name, value);
-        if (!constant) {
-            return {};
-        }
-        return { Function<T>(*constant) };
-    }
-
-    if (!value.HasMember("stops")) {
-        Log::Warning(Event::ParseStyle, "function must specify a function type");
-        return {};
-    }
-
-    float base = 1.0f;
-
-    if (value.HasMember("base")) {
-        const JSValue& value_base = value["base"];
-
-        if (!value_base.IsNumber()) {
-            Log::Warning(Event::ParseStyle, "base must be numeric");
-            return {};
-        }
-
-        base = value_base.GetDouble();
-    }
-
-    auto stops = parseStops<T>(name, value["stops"]);
-
-    if (!stops) {
-        return {};
-    }
-
-    return { Function<T>(*stops, base) };
-}
-
-template <> optional<Function<std::array<float, 2>>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<std::array<float, 2>>(name, value);
-}
-
-template <> optional<Function<std::string>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<std::string>(name, value);
-}
-
-template <> optional<Function<TranslateAnchorType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<TranslateAnchorType>(name, value);
-}
-
-template <> optional<Function<RotateAnchorType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<RotateAnchorType>(name, value);
-}
-
-template <> optional<Function<LineCapType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<LineCapType>(name, value);
-}
-
-template <> optional<Function<LineJoinType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<LineJoinType>(name, value);
-}
-
-template <> optional<Function<SymbolPlacementType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<SymbolPlacementType>(name, value);
-}
-
-template <> optional<Function<TextAnchorType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<TextAnchorType>(name, value);
-}
-
-template <> optional<Function<TextJustifyType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<TextJustifyType>(name, value);
-}
-
-template <> optional<Function<TextTransformType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<TextTransformType>(name, value);
-}
-
-template <> optional<Function<RotationAlignmentType>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<RotationAlignmentType>(name, value);
-}
-
-template <> optional<Function<bool>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<bool>(name, value);
-}
-
-template<> optional<Function<float>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<float>(name, value);
-}
-
-template<> optional<Function<Color>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<Color>(name, value);
-}
-
-template<> optional<Function<std::vector<float>>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<std::vector<float>>(name, value);
-}
-
-template<> optional<Function<std::vector<std::string>>> parseProperty(const char* name, const JSValue& value) {
-    return parseFunction<std::vector<std::string>>(name, value);
-}
-
 } // namespace mbgl
diff --git a/src/mbgl/style/property_parsing.hpp b/src/mbgl/style/property_parsing.hpp
index 73bc5a72c7..8deb58c00b 100644
--- a/src/mbgl/style/property_parsing.hpp
+++ b/src/mbgl/style/property_parsing.hpp
@@ -1,21 +1,109 @@
-#ifndef MBGL_PROPERTY_PARSING
-#define MBGL_PROPERTY_PARSING
+#pragma once
 
 #include <mbgl/style/types.hpp>
+#include <mbgl/style/function.hpp>
+#include <mbgl/style/property_transition.hpp>
 
 #include <mbgl/util/rapidjson.hpp>
 #include <mbgl/util/optional.hpp>
 
-#include <functional>
+#include <mbgl/platform/log.hpp>
+
+#include <string>
+#include <array>
+#include <vector>
 
 namespace mbgl {
 
 template <typename T>
-using optional = optional<T>;
+optional<T> parseConstant(const char* name, const JSValue&);
+
+template <> optional<bool> parseConstant(const char*, const JSValue&);
+template <> optional<float> parseConstant(const char*, const JSValue&);
+template <> optional<std::string> parseConstant(const char*, const JSValue&);
+template <> optional<Color> parseConstant(const char*, const JSValue&);
+template <> optional<TranslateAnchorType> parseConstant(const char*, const JSValue&);
+template <> optional<RotateAnchorType> parseConstant(const char*, const JSValue&);
+template <> optional<LineCapType> parseConstant(const char*, const JSValue&);
+template <> optional<LineJoinType> parseConstant(const char*, const JSValue&);
+template <> optional<SymbolPlacementType> parseConstant(const char*, const JSValue&);
+template <> optional<TextAnchorType> parseConstant(const char*, const JSValue&);
+template <> optional<TextJustifyType> parseConstant(const char*, const JSValue&);
+template <> optional<TextTransformType> parseConstant(const char*, const JSValue&);
+template <> optional<RotationAlignmentType> parseConstant(const char*, const JSValue&);
+template <> optional<std::array<float, 2>> parseConstant(const char*, const JSValue&);
+template <> optional<std::vector<float>> parseConstant(const char*, const JSValue&);
+template <> optional<std::vector<std::string>> parseConstant(const char*, const JSValue&);
 
 template <typename T>
-optional<T> parseProperty(const char* name, const JSValue&);
+optional<Function<T>> parseProperty(const char* name, const JSValue& value) {
+    if (!value.IsObject()) {
+        auto constant = parseConstant<T>(name, value);
 
-} // namespace mbgl
+        if (!constant) {
+            return {};
+        }
+
+        return { Function<T>(*constant) };
+    }
+
+    if (!value.HasMember("stops")) {
+        Log::Warning(Event::ParseStyle, "function must specify a function type");
+        return {};
+    }
+
+    float base = 1.0f;
+
+    if (value.HasMember("base")) {
+        const JSValue& value_base = value["base"];
+
+        if (!value_base.IsNumber()) {
+            Log::Warning(Event::ParseStyle, "base must be numeric");
+            return {};
+        }
+
+        base = value_base.GetDouble();
+    }
+
+    const JSValue& stopsValue = value["stops"];
+
+    if (!stopsValue.IsArray()) {
+        Log::Warning(Event::ParseStyle, "stops function must specify a stops array");
+        return {};
+    }
 
-#endif
+    std::vector<std::pair<float, T>> stops;
+
+    for (rapidjson::SizeType i = 0; i < stopsValue.Size(); ++i) {
+        const JSValue& stop = stopsValue[i];
+
+        if (!stop.IsArray()) {
+            Log::Warning(Event::ParseStyle, "function argument must be a numeric value");
+            return {};
+        }
+
+        if (stop.Size() != 2) {
+            Log::Warning(Event::ParseStyle, "stop must have zoom level and value specification");
+            return {};
+        }
+
+        const JSValue& z = stop[rapidjson::SizeType(0)];
+        if (!z.IsNumber()) {
+            Log::Warning(Event::ParseStyle, "zoom level in stop must be a number");
+            return {};
+        }
+
+        optional<T> v = parseConstant<T>(name, stop[rapidjson::SizeType(1)]);
+        if (!v) {
+            return {};
+        }
+
+        stops.emplace_back(z.GetDouble(), *v);
+    }
+
+    return { Function<T>(stops, base) };
+}
+
+optional<PropertyTransition> parsePropertyTransition(const char * name, const JSValue&);
+
+} // namespace mbgl