[core] Rationalize naming for style-related code

1 files changed, 38 insertions, 0 deletions

diff --git a/include/mbgl/style/property_value.hpp b/include/mbgl/style/property_value.hpp
new file mode 100644
index 0000000000..d8f83a0fb3
--- /dev/null
+++ b/include/mbgl/style/property_value.hpp
@@ -0,0 +1,38 @@
+#pragma once
+
+#include <mbgl/util/variant.hpp>
+#include <mbgl/style/function.hpp>
+
+namespace mbgl {
+namespace style {
+
+class Undefined {};
+
+template <class T>
+class PropertyValue {
+private:
+    using Value = variant<Undefined, T, Function<T>>;
+    Value value;
+
+public:
+    PropertyValue()                     : value()         {}
+    PropertyValue(         T  constant) : value(constant) {}
+    PropertyValue(Function<T> function) : value(function) {}
+
+    bool isUndefined() const { return value.which() == 0; }
+    bool isConstant()  const { return value.which() == 1; }
+    bool isFunction()  const { return value.which() == 2; }
+
+    const          T & asConstant() const { return value.template get<         T >(); }
+    const Function<T>& asFunction() const { return value.template get<Function<T>>(); }
+
+    explicit operator bool() const { return !isUndefined(); };
+
+    template <typename Visitor>
+    static auto visit(const PropertyValue<T>& value, Visitor&& visitor) {
+        return Value::visit(value.value, visitor);
+    }
+};
+
+} // namespace style
+} // namespace mbgl