types/traits: add the identity type function

types/traits.hpp

@@ -56,6 +56,22 @@ namespace util {
 }
 
 
+namespace util::types {
+    ///////////////////////////////////////////////////////////////////////////
+    /// CXX20: An early implementation of std::identity_t and related
+    /// structures; useful for disabling template argument deduction, and
+    /// higher order template functions.
+    template <typename T>
+    struct identity { using type = T; };
+
+
+    //-------------------------------------------------------------------------
+    template <typename T>
+    using identity_t = typename identity<T>::type;
+}
+
+
+
 ///////////////////////////////////////////////////////////////////////////////
 template <typename T> struct is_dereferencable     : std::false_type { };
 template <typename T> struct is_dereferencable<T*> : std::true_type  { };