1 files changed, 34 insertions, 0 deletions
diff --git a/include/mbgl/style/expression/coercion.hpp b/include/mbgl/style/expression/coercion.hpp
new file mode 100644
index 0000000000..665bb7ce7c
--- /dev/null
+++ b/include/mbgl/style/expression/coercion.hpp
@@ -0,0 +1,34 @@
+#pragma once
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/conversion.hpp>
+#include <memory>
+#include <vector>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+/**
+ * Special form for error-coalescing coercion expressions "to-number",
+ * "to-color".  Since these coercions can fail at runtime, they accept multiple
+ * arguments, only evaluating one at a time until one succeeds.
+ */
+class Coercion : public Expression  {
+public:
+    Coercion(type::Type type_, std::vector<std::unique_ptr<Expression>> inputs_);
+
+    static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);
+
+    EvaluationResult evaluate(const EvaluationContext& params) const override;
+    void eachChild(const std::function<void(const Expression&)>& visit) const override;
+
+    bool operator==(const Expression& e) const override;
+private:
+    EvaluationResult (*coerceSingleValue) (const Value& v);
+    std::vector<std::unique_ptr<Expression>> inputs;
+};
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl
+