1 files changed, 55 insertions, 0 deletions
diff --git a/src/mbgl/style/function_properties.hpp b/src/mbgl/style/function_properties.hpp
new file mode 100644
index 0000000000..924f192330
--- /dev/null
+++ b/src/mbgl/style/function_properties.hpp
@@ -0,0 +1,55 @@
+#ifndef MBGL_STYLE_FUNCTION_PROPERTIES
+#define MBGL_STYLE_FUNCTION_PROPERTIES
+
+#include <mbgl/util/variant.hpp>
+
+#include <vector>
+
+namespace mbgl {
+
+template <typename T>
+struct ConstantFunction {
+    inline ConstantFunction(const T &value_) : value(value_) {}
+    inline T evaluate(float) const { return value; }
+
+private:
+    const T value;
+};
+
+template <typename T>
+struct StopsFunction {
+    inline StopsFunction(const std::vector<std::pair<float, T>> &values_, float base_) : values(values_), base(base_) {}
+    T evaluate(float z) const;
+
+private:
+    const std::vector<std::pair<float, T>> values;
+    const float base;
+};
+
+template <typename T>
+using Function = mapbox::util::variant<
+    std::false_type,
+    ConstantFunction<T>,
+    StopsFunction<T>
+>;
+
+template <typename T>
+struct FunctionEvaluator {
+    typedef T result_type;
+    inline FunctionEvaluator(float z_) : z(z_) {}
+
+    inline result_type operator()(const std::false_type &) {
+        return result_type();
+    }
+
+    template <template <typename> class Fn>
+    inline result_type operator()(const Fn<T>& fn) {
+        return fn.evaluate(z);
+    }
+private:
+    float z;
+};
+
+}
+
+#endif