[core] Introduce PropertyValue<T>

PropertyValue<T> represents the three possible types of style property value: undefined, constant, or function.

1 files changed, 22 insertions, 8 deletions

diff --git a/src/mbgl/style/layout_property.hpp b/src/mbgl/style/layout_property.hpp
index a856e7589c..b4857aeae5 100644
--- a/src/mbgl/style/layout_property.hpp
+++ b/src/mbgl/style/layout_property.hpp
@@ -1,7 +1,8 @@
 #pragma once
 
+#include <mbgl/style/property_value.hpp>
 #include <mbgl/style/property_parsing.hpp>
-#include <mbgl/style/function_evaluator.hpp>
+#include <mbgl/style/property_evaluator.hpp>
 #include <mbgl/util/rapidjson.hpp>
 
 #include <utility>
@@ -11,25 +12,38 @@ namespace mbgl {
 template <typename T>
 class LayoutProperty {
 public:
-    explicit LayoutProperty(T v) : value(std::move(v)) {}
+    explicit LayoutProperty(T v)
+        : value(std::move(v)),
+          defaultValue(value) {}
+
+    const PropertyValue<T>& get() const {
+        return currentValue;
+    }
+
+    void set(const PropertyValue<T>& value_) {
+        currentValue = value_;
+    }
 
     void parse(const char * name, const JSValue& layout) {
         if (layout.HasMember(name)) {
-            parsedValue = parseProperty<T>(name, layout[name]);
+            currentValue = parseProperty<T>(name, layout[name]);
         }
     }
 
     void calculate(const StyleCalculationParameters& parameters) {
-        if (parsedValue) {
-            NormalFunctionEvaluator<T> evaluator;
-            value = evaluator(*parsedValue, parameters);
+        if (currentValue) {
+            PropertyEvaluator<T> evaluator(parameters, defaultValue);
+            value = PropertyValue<T>::visit(currentValue, evaluator);
         }
     }
 
+    // TODO: remove / privatize
     operator T() const { return value; }
-
-    optional<Function<T>> parsedValue;
     T value;
+
+private:
+    T defaultValue;
+    PropertyValue<T> currentValue;
 };
 
 } // namespace mbgl