From 8a53139f94bdea60099723528079a6a514764f3a Mon Sep 17 00:00:00 2001
From: Frank Stein <dr.frank.stain@gmail.com>
Date: Sat, 22 Oct 2016 00:04:15 +0200
Subject: std::hash for const Entity implemented.

---
 entityx/Entity.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/entityx/Entity.h b/entityx/Entity.h
index 9fcf676..e4a3871 100644
--- a/entityx/Entity.h
+++ b/entityx/Entity.h
@@ -1079,5 +1079,11 @@ template <> struct hash<entityx::Entity> {
     return static_cast<std::size_t>(entity.id().index() ^ entity.id().version());
   }
 };
+
+template <> struct hash<const entityx::Entity> {
+  std::size_t operator () (const entityx::Entity &entity) const {
+    return static_cast<std::size_t>(entity.id().index() ^ entity.id().version());
+  }
+};
 }
 
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