1 files changed, 40 insertions, 0 deletions
diff --git a/src/mbgl/style/expression/is_constant.cpp b/src/mbgl/style/expression/is_constant.cpp
new file mode 100644
index 0000000000..0ebb37faa9
--- /dev/null
+++ b/src/mbgl/style/expression/is_constant.cpp
@@ -0,0 +1,40 @@
+#include <mbgl/style/expression/is_constant.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+bool isFeatureConstant(const Expression& expression) {
+    if (auto e = dynamic_cast<const CompoundExpressionBase*>(&expression)) {
+        const std::string name = e->getName();
+        optional<std::size_t> parameterCount = e->getParameterCount();
+        if (name == "get" && parameterCount && *parameterCount == 1) {
+            return false;
+        } else if (name == "has" && parameterCount && *parameterCount == 1) {
+            return false;
+        } else if (
+            name == "properties" ||
+            name == "geometry-type" ||
+            name == "id"
+        ) {
+            return false;
+        }
+    }
+
+    bool featureConstant = true;
+    expression.eachChild([&](const Expression& e) {
+        if (featureConstant && !isFeatureConstant(e)) {
+            featureConstant = false;
+        }
+    });
+    return featureConstant;
+}
+
+bool isZoomConstant(const Expression& e) {
+    return isGlobalPropertyConstant(e, std::array<std::string, 1>{{"zoom"}});
+}
+
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl