1 // Copyright 2023 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_TYPES_IS_INSTANTIATION_H_ 6 #define BASE_TYPES_IS_INSTANTIATION_H_ 7 8 #include <type_traits> 9 10 namespace base { 11 namespace internal { 12 13 // True if and only if `T` is `C<Types...>` for some set of types, i.e. `T` is 14 // an instantiation of the template `C`. 15 // 16 // This is false by default. We specialize it to true below for pairs of 17 // arguments that satisfy the condition. 18 template <template <typename...> class C, typename T> 19 inline constexpr bool is_instantiation_v = false; 20 21 template <template <typename...> class C, typename... Ts> 22 inline constexpr bool is_instantiation_v<C, C<Ts...>> = true; 23 24 } // namespace internal 25 26 // True if and only if the type `T` is an instantiation of the template `C` with 27 // some set of type arguments. 28 // 29 // Note that there is no allowance for reference or const/volatile qualifiers; 30 // if these are a concern you probably want to feed through `std::decay_t<T>`. 31 template <template <typename...> class C, typename T> 32 concept is_instantiation = internal::is_instantiation_v<C, T>; 33 34 } // namespace base 35 36 #endif // BASE_TYPES_IS_INSTANTIATION_H_ 37