libcxx/include/__algorithm/unwrap_iter.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_UNWRAP_ITER_H
  10 #define _LIBCPP___ALGORITHM_UNWRAP_ITER_H
  11
  12 #include <__config>
  13 #include <__iterator/iterator_traits.h>
  14 #include <__memory/pointer_traits.h>
  15 #include <__type_traits/enable_if.h>
  16 #include <__type_traits/is_constructible.h>
  17 #include <__utility/declval.h>
  18 #include <__utility/move.h>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_PUSH_MACROS
  25 #include <__undef_macros>
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 // TODO: Change the name of __unwrap_iter_impl to something more appropriate
  30 // The job of __unwrap_iter is to remove iterator wrappers (like reverse_iterator or __wrap_iter),
  31 // to reduce the number of template instantiations and to enable pointer-based optimizations e.g. in std::copy.
  32 //
  33 // Some algorithms (e.g. std::copy, but not std::sort) need to convert an
  34 // "unwrapped" result back into the original iterator type. Doing that is the job of __rewrap_iter.
  35
  36 // Default case - we can't unwrap anything
  37 template <class _Iter, bool = __libcpp_is_contiguous_iterator<_Iter>::value>
  38 struct __unwrap_iter_impl {
  39   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter, _Iter __iter) { return __iter; }
  40   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __unwrap(_Iter __i) _NOEXCEPT { return __i; }
  41 };
  42
  43 // TODO(hardening): make sure that the following unwrapping doesn't unexpectedly turn hardened iterators into raw
  44 // pointers.
  45
  46 // It's a contiguous iterator, so we can use a raw pointer instead
  47 template <class _Iter>
  48 struct __unwrap_iter_impl<_Iter, true> {
  49   using _ToAddressT = decltype(std::__to_address(std::declval<_Iter>()));
  50
  51   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter __orig_iter, _ToAddressT __unwrapped_iter) {
  52     return __orig_iter + (__unwrapped_iter - std::__to_address(__orig_iter));
  53   }
  54
  55   static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ToAddressT __unwrap(_Iter __i) _NOEXCEPT {
  56     return std::__to_address(__i);
  57   }
  58 };
  59
  60 template <class _Iter,
  61           class _Impl                                             = __unwrap_iter_impl<_Iter>,
  62           __enable_if_t<is_copy_constructible<_Iter>::value, int> = 0>
  63 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 decltype(_Impl::__unwrap(std::declval<_Iter>()))
  64 __unwrap_iter(_Iter __i) _NOEXCEPT {
  65   return _Impl::__unwrap(__i);
  66 }
  67
  68 // Allow input_iterators to be passed to __unwrap_iter (but not __rewrap_iter)
  69 #if _LIBCPP_STD_VER >= 20
  70 template <class _Iter, __enable_if_t<!is_copy_constructible<_Iter>::value, int> = 0>
  71 inline _LIBCPP_HIDE_FROM_ABI constexpr _Iter __unwrap_iter(_Iter __i) noexcept {
  72   return __i;
  73 }
  74 #endif
  75
  76 template <class _OrigIter, class _Iter, class _Impl = __unwrap_iter_impl<_OrigIter> >
  77 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _OrigIter __rewrap_iter(_OrigIter __orig_iter, _Iter __iter) _NOEXCEPT {
  78   return _Impl::__rewrap(std::move(__orig_iter), std::move(__iter));
  79 }
  80
  81 _LIBCPP_END_NAMESPACE_STD
  82
  83 _LIBCPP_POP_MACROS
  84
  85 #endif // _LIBCPP___ALGORITHM_UNWRAP_ITER_H