1 /* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ART_LIBARTBASE_BASE_STL_UTIL_IDENTITY_H_ 18 #define ART_LIBARTBASE_BASE_STL_UTIL_IDENTITY_H_ 19 20 namespace art { 21 22 // Use to suppress type deduction for a function argument. 23 // See std::identity<> for more background: 24 // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1856.html#20.2.2 - move/forward helpers 25 // 26 // e.g. "template <typename X> void bar(identity<X>::type foo); 27 // bar(5); // compilation error 28 // bar<int>(5); // ok 29 // or "template <typename T> void foo(T* x, typename Identity<T*>::type y); 30 // Base b; 31 // Derived d; 32 // foo(&b, &d); // Use implicit Derived* -> Base* conversion. 33 // If T was deduced from both &b and &d, there would be a mismatch, i.e. deduction failure. 34 template <typename T> 35 struct Identity { 36 using type = T; 37 }; 38 39 } // namespace art 40 41 #endif // ART_LIBARTBASE_BASE_STL_UTIL_IDENTITY_H_ 42
