| // -*- C++ -*- |
| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| #ifndef _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H |
| #define _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H |
| |
| #include <__config> |
| #include <__iterator/concepts.h> // indirectly_readable |
| #include <__iterator/iterator_traits.h> // iter_reference_t |
| #include <__memory/addressof.h> |
| #include <concepts> // constructible_from |
| #include <optional> |
| #include <type_traits> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| #pragma GCC system_header |
| #endif |
| |
| _LIBCPP_PUSH_MACROS |
| #include <__undef_macros> |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| // clang-format off |
| |
| #if !defined(_LIBCPP_HAS_NO_RANGES) |
| |
| namespace ranges { |
| // __non_propagating_cache is a helper type that allows storing an optional value in it, |
| // but which does not copy the source's value when it is copy constructed/assigned to, |
| // and which resets the source's value when it is moved-from. |
| // |
| // This type is used as an implementation detail of some views that need to cache the |
| // result of `begin()` in order to provide an amortized O(1) begin() method. Typically, |
| // we don't want to propagate the value of the cache upon copy because the cached iterator |
| // may refer to internal details of the source view. |
| template<class _Tp> |
| requires is_object_v<_Tp> |
| class _LIBCPP_TEMPLATE_VIS __non_propagating_cache { |
| optional<_Tp> __value_ = nullopt; |
| |
| public: |
| _LIBCPP_HIDE_FROM_ABI __non_propagating_cache() = default; |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr __non_propagating_cache(__non_propagating_cache const&) noexcept |
| : __value_(nullopt) |
| { } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr __non_propagating_cache(__non_propagating_cache&& __other) noexcept |
| : __value_(nullopt) |
| { |
| __other.__value_.reset(); |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr __non_propagating_cache& operator=(__non_propagating_cache const& __other) noexcept { |
| if (this != _VSTD::addressof(__other)) { |
| __value_.reset(); |
| } |
| return *this; |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr __non_propagating_cache& operator=(__non_propagating_cache&& __other) noexcept { |
| __value_.reset(); |
| __other.__value_.reset(); |
| return *this; |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr _Tp& operator*() { return *__value_; } |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr _Tp const& operator*() const { return *__value_; } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr bool __has_value() const { return __value_.has_value(); } |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr void __set(_Tp const& __value) { __value_.emplace(__value); } |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr void __set(_Tp&& __value) { __value_.emplace(_VSTD::move(__value)); } |
| }; |
| |
| struct __empty_cache { }; |
| } // namespace ranges |
| |
| #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_RANGES) |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| _LIBCPP_POP_MACROS |
| |
| #endif // _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H |