1 // Copyright 2022 The Abseil Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ 16 #define ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ 17 18 #include <type_traits> 19 #include <utility> 20 21 #include "absl/strings/string_view.h" 22 23 namespace absl { 24 ABSL_NAMESPACE_BEGIN 25 26 namespace strings_internal { 27 28 // This is an empty class not intended to be used. It exists so that 29 // `HasAbslStringify` can reference a universal class rather than needing to be 30 // copied for each new sink. 31 class UnimplementedSink { 32 public: 33 void Append(size_t count, char ch); 34 35 void Append(string_view v); 36 37 // Support `absl::Format(&sink, format, args...)`. 38 friend void AbslFormatFlush(UnimplementedSink* sink, absl::string_view v); 39 }; 40 41 } // namespace strings_internal 42 43 // `HasAbslStringify<T>` detects if type `T` supports the `AbslStringify()` 44 // customization point (see 45 // https://abseil.io/docs/cpp/guides/format#abslstringify for the 46 // documentation). 47 // 48 // Note that there are types that can be `StrCat`-ed that do not use the 49 // `AbslStringify` customization point (for example, `int`). 50 51 template <typename T, typename = void> 52 struct HasAbslStringify : std::false_type {}; 53 54 template <typename T> 55 struct HasAbslStringify< 56 T, std::enable_if_t<std::is_void<decltype(AbslStringify( 57 std::declval<strings_internal::UnimplementedSink&>(), 58 std::declval<const T&>()))>::value>> : std::true_type {}; 59 60 ABSL_NAMESPACE_END 61 } // namespace absl 62 63 #endif // ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ 64