You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
73 lines
2.6 KiB
73 lines
2.6 KiB
// |
|
// 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 |
|
// |
|
// 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_INTERNAL_RESIZE_UNINITIALIZED_H_ |
|
#define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |
|
|
|
#include <string> |
|
#include <type_traits> |
|
#include <utility> |
|
|
|
#include "absl/base/port.h" |
|
#include "absl/meta/type_traits.h" // for void_t |
|
|
|
namespace absl { |
|
ABSL_NAMESPACE_BEGIN |
|
namespace strings_internal { |
|
|
|
// Is a subclass of true_type or false_type, depending on whether or not |
|
// T has a __resize_default_init member. |
|
template <typename string_type, typename = void> |
|
struct ResizeUninitializedTraits { |
|
using HasMember = std::false_type; |
|
static void Resize(string_type* s, size_t new_size) { s->resize(new_size); } |
|
}; |
|
|
|
// __resize_default_init is provided by libc++ >= 8.0 |
|
template <typename string_type> |
|
struct ResizeUninitializedTraits< |
|
string_type, absl::void_t<decltype(std::declval<string_type&>() |
|
.__resize_default_init(237))> > { |
|
using HasMember = std::true_type; |
|
static void Resize(string_type* s, size_t new_size) { |
|
s->__resize_default_init(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 ResizeUninitializedTraits<string_type>::HasMember::value; |
|
} |
|
|
|
// 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. |
|
template <typename string_type, typename = void> |
|
inline void STLStringResizeUninitialized(string_type* s, size_t new_size) { |
|
ResizeUninitializedTraits<string_type>::Resize(s, new_size); |
|
} |
|
|
|
} // namespace strings_internal |
|
ABSL_NAMESPACE_END |
|
} // namespace absl |
|
|
|
#endif // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
|
|
|