etl/type_traits.h: Add support for type_identity (#905)

* etl/type_traits.h: Add support for type_identity

* test/test_type_traits.cpp: Add a test for etl::type_identity (type_identity_test_add(1.5f, 2) == 3.5f)

* Update test_type_traits.cpp

Use CHECK_CLOSE instead of CHECK for equality

include/etl/generators/type_traits_generator.h

@@ -2295,6 +2295,17 @@ typedef integral_constant<bool, true>  true_type;
   template <typename T>
   using signed_type_t = typename signed_type<T>::type;
 #endif
+
+//*********************************************
+// type_identity
+
+template <typename T>
+struct type_identity { typedef T type; };
+
+#if ETL_USING_CPP11
+  template <typename T>
+  using type_identity_t = typename type_identity<T>::type;
+#endif
 }
 
 // Helper macros

include/etl/type_traits.h

@@ -2288,6 +2288,17 @@ typedef integral_constant<bool, true>  true_type;
   template <typename T>
   using signed_type_t = typename signed_type<T>::type;
 #endif
+
+//*********************************************
+// type_identity
+
+template <typename T>
+struct type_identity { typedef T type; };
+
+#if ETL_USING_CPP11
+  template <typename T>
+  using type_identity_t = typename type_identity<T>::type;
+#endif
 }
 
 // Helper macros

test/test_type_traits.cpp

@@ -122,6 +122,13 @@ namespace
     NotDefaultConstructible(NotDefaultConstructible&&) = delete;
     NotDefaultConstructible& operator =(NotDefaultConstructible&) = delete;
   };
+
+  // A function to test etl::type_identity.
+  template <typename T>
+  T type_identity_test_add(T first, typename etl::type_identity<T>::type second)
+  {
+    return first + second;
+  }
 }
 
 // Definitions for when the STL and compiler built-ins are not available.
@@ -1320,4 +1327,9 @@ namespace
     CHECK_FALSE(bool(etl::is_base_of_all<Base, D1, D2, D3, D4>::value));
 #endif
   }
+
+  //*************************************************************************
+  TEST(test_type_identity) {
+    CHECK_CLOSE(type_identity_test_add(1.5f, 2), 3.5f, 0.01f);
+  }
 }