include/o3tl/span.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  */
   9
  10 #ifndef INCLUDED_O3TL_SPAN_HXX
  11 #define INCLUDED_O3TL_SPAN_HXX
  12
  13 #include <sal/config.h>
  14
  15 #if __has_include(<span>)
  16
  17 #include <span>
  18
  19 namespace o3tl { using std::span; }
  20
  21 #else
  22
  23 #include <cassert>
  24 #include <cstddef>
  25 #include <iterator>
  26
  27 namespace o3tl {
  28
  29 /** A barebones approximation of C++20 <span>.
  30 */
  31 template<typename T>
  32 class span {
  33 public:
  34     using value_type = T;
  35     using pointer = value_type *;
  36     using const_pointer = value_type const *;
  37     using reference = value_type &;
  38     using const_reference = value_type const &;
  39     using const_iterator = const_pointer;
  40     using iterator = pointer;
  41     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
  42     using reverse_iterator = std::reverse_iterator<iterator>;
  43     using index_type = std::size_t;
  44     using difference_type = std::ptrdiff_t;
  45
  46     constexpr span() noexcept : data_(nullptr), size_(0) {}
  47
  48     template<std::size_t N>
  49     constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}
  50
  51     constexpr span (T *a, index_type len) noexcept
  52         : data_(a), size_(len)
  53     {
  54         // not terribly sure about this, might need to strengthen it
  55         assert(a != nullptr || len == 0);
  56     }
  57
  58     constexpr bool empty() const noexcept { return size_ == 0; }
  59
  60     constexpr iterator begin() const noexcept { return data_; }
  61     constexpr iterator end() const noexcept { return begin() + size(); }
  62
  63     constexpr const_iterator cbegin() const noexcept { return begin(); }
  64     constexpr const_iterator cend() const noexcept { return end(); }
  65
  66     reverse_iterator rbegin() const noexcept
  67     { return reverse_iterator(end()); }
  68     reverse_iterator rend() const noexcept
  69     { return reverse_iterator(begin()); }
  70
  71     constexpr const_reverse_iterator crbegin() const noexcept
  72     { return rbegin(); }
  73     constexpr const_reverse_iterator crend() const noexcept { return rend(); }
  74
  75     constexpr index_type size() const noexcept { return size_; }
  76
  77     constexpr reference operator [](index_type pos) const {
  78         assert(pos < size());
  79         return data_[pos];
  80     }
  81
  82     constexpr pointer data() const noexcept { return data_; }
  83
  84 private:
  85     pointer    data_;
  86     index_type size_;
  87 };
  88
  89 } // namespace o3tl
  90
  91 #endif
  92
  93 #endif
  94
  95 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */