has_absl_stringify.h

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// Copyright 2022 The Abseil Authors

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//     https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#ifndef ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_

#define ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_

#include <type_traits>

#include <utility>

#include "absl/strings/string_view.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace strings_internal {

// This is an empty class not intended to be used. It exists so that

// `HasAbslStringify` can reference a universal class rather than needing to be

// copied for each new sink.

class UnimplementedSink {

 public:

  void Append(size_t count, char ch);

  void Append(string_view v);

  // Support `absl::Format(&sink, format, args...)`.

  friend void AbslFormatFlush(UnimplementedSink* sink, absl::string_view v);

};

}  // namespace strings_internal

// `HasAbslStringify<T>` detects if type `T` supports the `AbslStringify()`

// customization point (see

// https://abseil.io/docs/cpp/guides/format#abslstringify for the

// documentation).

//

// Note that there are types that can be `StrCat`-ed that do not use the

// `AbslStringify` customization point (for example, `int`).

template <typename T, typename = void>

struct HasAbslStringify : std::false_type {};

template <typename T>

struct HasAbslStringify<

    T, std::enable_if_t<std::is_void<decltype(AbslStringify(

           std::declval<strings_internal::UnimplementedSink&>(),

           std::declval<const T&>()))>::value>> : std::true_type {};

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_