hash/mix: add a simple std compatible wrapper for hash::mix

CMakeLists.txt

@@ -412,6 +412,8 @@ list (
     hash/fnv1a.hpp
     hash/halfsipmix.cpp
     hash/halfsipmix.hpp
+    hash/mix.cpp
+    hash/mix.hpp
     hash/murmur/common.cpp
     hash/murmur/common.hpp
     hash/murmur.hpp

hash/mix.cpp

@@ -0,0 +1 @@
+#include "./mix.hpp"

hash/mix.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "../hash.hpp"
+
+#include <utility>
+
+
+namespace cruft::hash {
+    /// A std compatible adapter for a variadic 'mix' hash.
+    ///
+    /// It combines multiple values in a way that is unlikely to result in collisions.
+    ///
+    /// The exact implementation is not defined.
+    struct mixer {
+        template <typename ...ValueT>
+        auto operator () (ValueT &&...elements)
+        {
+            return cruft::hash::mix (
+                std::forward<ValueT> (elements)...
+            );
+        }
+    };
+}