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 #include <config_global.h>
  16
  17 #if HAVE_CPP_SPAN
  18
  19 #include <span>
  20
  21 namespace o3tl { using std::span; }
  22
  23 #else
  24
  25 #include <cassert>
  26 #include <cstddef>
  27 #include <iterator>
  28 #include <type_traits>
  29 #include <vector>
  30
  31 namespace o3tl {
  32
  33 /** A barebones approximation of C++20 <span>.
  34 */
  35 template<typename T>
  36 class span {
  37 public:
  38     using value_type = T;
  39     using pointer = value_type *;
  40     using const_pointer = value_type const *;
  41     using reference = value_type &;
  42     using const_reference = value_type const &;
  43     using const_iterator = const_pointer;
  44     using iterator = pointer;
  45     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
  46     using reverse_iterator = std::reverse_iterator<iterator>;
  47     using size_type = std::size_t;
  48     using difference_type = std::ptrdiff_t;
  49
  50     constexpr span() noexcept : data_(nullptr), size_(0) {}
  51
  52     template<std::size_t N>
  53     constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}
  54
  55     constexpr span (T *a, size_type len) noexcept
  56         : data_(a), size_(len)
  57     {
  58         // not terribly sure about this, might need to strengthen it
  59         assert(a != nullptr || len == 0);
  60     }
  61
  62     template<typename T2>
  63     constexpr span(const std::vector<T2>& vec)
  64         : data_(vec.data()), size_(vec.size()) {}
  65
  66     /** for assigning from span<T> to span<const T> */
  67     constexpr span (const span<typename std::remove_const<T>::type>& other) noexcept
  68         : data_(other.data()), size_(other.size()) {}
  69
  70     constexpr bool empty() const noexcept { return size_ == 0; }
  71
  72     constexpr iterator begin() const noexcept { return data_; }
  73     constexpr iterator end() const noexcept { return begin() + size(); }
  74
  75     reverse_iterator rbegin() const noexcept
  76     { return reverse_iterator(end()); }
  77     reverse_iterator rend() const noexcept
  78     { return reverse_iterator(begin()); }
  79
  80     constexpr size_type size() const noexcept { return size_; }
  81
  82     constexpr reference operator [](size_type pos) const {
  83         assert(pos < size());
  84         return data_[pos];
  85     }
  86
  87     constexpr pointer data() const noexcept { return data_; }
  88
  89 private:
  90     pointer    data_;
  91     size_type size_;
  92 };
  93
  94 } // namespace o3tl
  95
  96 #endif
  97
  98 #endif
  99
 100 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */