From ca8f32a914ad724bab08b0bb1f930126b4fa8ce5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Konstantin=20K=C3=A4fer?= <mail@kkaefer.com>
Date: Thu, 15 Sep 2016 12:46:52 +0200
Subject: [PATCH] [core] add explicit std::hash<mbgl::style::ClassID>
 implementation to appease GCC

---
 src/mbgl/style/class_dictionary.hpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/mbgl/style/class_dictionary.hpp b/src/mbgl/style/class_dictionary.hpp
index c95773d7c..e609fb530 100644
--- a/src/mbgl/style/class_dictionary.hpp
+++ b/src/mbgl/style/class_dictionary.hpp
@@ -3,6 +3,7 @@
 #include <cstdint>
 #include <string>
 #include <unordered_map>
+#include <functional>
 
 namespace mbgl {
 namespace style {
@@ -34,3 +35,19 @@ private:
 
 } // namespace style
 } // namespace mbgl
+
+namespace std {
+
+// Explicitly define std::hash<style::ClassID> because GCC doesn't automatically use std::hash<> of
+// the underlying enum type.
+
+template <>
+struct hash<mbgl::style::ClassID> {
+public:
+    size_t operator()(const mbgl::style::ClassID id) const {
+        using T = std::underlying_type_t<mbgl::style::ClassID>;
+        return std::hash<T>()(static_cast<T>(id));
+    }
+};
+
+} // namespace std