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//
// Copyright 2017 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
//
// http://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_INTERNAL_RESIZE_UNINITIALIZED_H_
#define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
#include <string>
#include <utility>
#include "absl/base/port.h"
#include "absl/meta/type_traits.h" // for void_t
namespace absl {
namespace strings_internal {
// Is a subclass of true_type or false_type, depending on whether or not
// T has a resize_uninitialized member.
template <typename T, typename = void>
struct HasResizeUninitialized : std::false_type {};
template <typename T>
struct HasResizeUninitialized<
T, absl::void_t<decltype(std::declval<T>().resize_uninitialized(237))>>
: std::true_type {};
template <typename string_type>
void ResizeUninit(string_type* s, size_t new_size, std::true_type) {
s->resize_uninitialized(new_size);
}
template <typename string_type>
void ResizeUninit(string_type* s, size_t new_size, std::false_type) {
s->resize(new_size);
}
// Returns true if the std::string implementation supports a resize where
// the new characters added to the std::string are left untouched.
//
// (A better name might be "STLStringSupportsUninitializedResize", alluding to
// the previous function.)
template <typename string_type>
inline constexpr bool STLStringSupportsNontrashingResize(string_type*) {
return HasResizeUninitialized<string_type>();
}
// Like str->resize(new_size), except any new characters added to "*str" as a
// result of resizing may be left uninitialized, rather than being filled with
// '0' bytes. Typically used when code is then going to overwrite the backing
// store of the std::string with known data. Uses a Google extension to std::string.
template <typename string_type, typename = void>
inline void STLStringResizeUninitialized(string_type* s, size_t new_size) {
ResizeUninit(s, new_size, HasResizeUninitialized<string_type>());
}
} // namespace strings_internal
} // namespace absl
#endif // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
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