1 files changed, 51 insertions, 0 deletions
diff --git a/include/mbgl/style/data_driven_property_value.hpp b/include/mbgl/style/data_driven_property_value.hpp
new file mode 100644
index 0000000000..4653224f15
--- /dev/null
+++ b/include/mbgl/style/data_driven_property_value.hpp
@@ -0,0 +1,51 @@
+#pragma once
+
+#include <mbgl/util/variant.hpp>
+#include <mbgl/style/undefined.hpp>
+#include <mbgl/style/function/camera_function.hpp>
+#include <mbgl/style/function/source_function.hpp>
+#include <mbgl/style/function/composite_function.hpp>
+
+namespace mbgl {
+namespace style {
+
+template <class T>
+class DataDrivenPropertyValue {
+private:
+    using Value = variant<
+        Undefined,
+        T,
+        CameraFunction<T>,
+        SourceFunction<T>,
+        CompositeFunction<T>>;
+
+    Value value;
+
+    friend bool operator==(const DataDrivenPropertyValue& lhs,
+                           const DataDrivenPropertyValue& rhs) {
+        return lhs.value == rhs.value;
+    }
+
+public:
+    DataDrivenPropertyValue() = default;
+    DataDrivenPropertyValue(                  T  v) : value(std::move(v)) {}
+    DataDrivenPropertyValue(   CameraFunction<T> v) : value(std::move(v)) {}
+    DataDrivenPropertyValue(   SourceFunction<T> v) : value(std::move(v)) {}
+    DataDrivenPropertyValue(CompositeFunction<T> v) : value(std::move(v)) {}
+
+    bool isUndefined() const {
+        return value.template is<Undefined>();
+    }
+
+    bool isDataDriven() const {
+        return value.template is<SourceFunction<T>>() || value.template is<CompositeFunction<T>>();
+    }
+
+    template <typename Evaluator>
+    auto evaluate(const Evaluator& evaluator) const {
+        return Value::visit(value, evaluator);
+    }
+};
+
+} // namespace style
+} // namespace mbgl