1 files changed, 16 insertions, 15 deletions
diff --git a/include/mbgl/style/function.hpp b/include/mbgl/style/function.hpp
index 97e880b280..b023229e4f 100644
--- a/include/mbgl/style/function.hpp
+++ b/include/mbgl/style/function.hpp
@@ -1,7 +1,8 @@
 #pragma once
 
-#include <vector>
+#include <cassert>
 #include <utility>
+#include <vector>
 
 namespace mbgl {
 namespace style {
@@ -12,28 +13,28 @@ public:
     using Stop = std::pair<float, T>;
     using Stops = std::vector<Stop>;
 
-    explicit Function(Stops stops_, float base_)
-        : base(base_), stops(std::move(stops_)) {}
+    Function(Stops stops_, float base_)
+        : base(base_), stops(std::move(stops_)) {
+        assert(stops.size() > 0);
+    }
 
     float getBase() const { return base; }
     const std::vector<std::pair<float, T>>& getStops() const { return stops; }
 
+    T evaluate(float z) const;
+
+    friend bool operator==(const Function& lhs, const Function& rhs) {
+        return lhs.base == rhs.base && lhs.stops == rhs.stops;
+    }
+
+    friend bool operator!=(const Function& lhs, const Function& rhs) {
+        return !(lhs == rhs);
+    }
+
 private:
     float base = 1;
     std::vector<std::pair<float, T>> stops;
-
-    template <class S> friend bool operator==(const Function<S>&, const Function<S>&);
 };
 
-template <class T>
-bool operator==(const Function<T>& lhs, const Function<T>& rhs) {
-    return lhs.base == rhs.base && lhs.stops == rhs.stops;
-}
-
-template <class T>
-bool operator!=(const Function<T>& lhs, const Function<T>& rhs) {
-    return !(lhs == rhs);
-}
-
 } // namespace style
 } // namespace mbgl