1 files changed, 35 insertions, 0 deletions
diff --git a/include/mbgl/style/expression/is_constant.hpp b/include/mbgl/style/expression/is_constant.hpp
new file mode 100644
index 0000000000..29e03ccbc0
--- /dev/null
+++ b/include/mbgl/style/expression/is_constant.hpp
@@ -0,0 +1,35 @@
+#pragma once
+
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/expression/compound_expression.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+template <typename T>
+bool isGlobalPropertyConstant(const Expression& expression, const T& properties) {
+    if (auto e = dynamic_cast<const CompoundExpressionBase*>(&expression)) {
+        for (const std::string& property : properties) {
+            if (e->getName() == property) {
+                return false;
+            }
+        }
+    }
+    
+    bool isConstant = true;
+    expression.eachChild([&](const Expression& e) {
+        if (isConstant && !isGlobalPropertyConstant(e, properties)) {
+            isConstant = false;
+        }
+    });
+    return isConstant;
+};
+
+bool isFeatureConstant(const Expression& expression);
+bool isZoomConstant(const Expression& e);
+
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl