array_view was changed to span in upcoming C++20

...see <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0122r7.pdf>
"span: bounds-safe views for sequences of objects".  o3tl::span is still an
incomplete approximation of std::span; removed those o3tl::array_view members
that are not present in std::span (and were not used in the code).

Relies on C++17 __has_include to use standard <span> where available (e.g., in
LLVM 7 libc++).

Change-Id: I82a7e246b61b2456fa6183025d25eec4121ad3c9
Reviewed-on: https://gerrit.libreoffice.org/66215
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 95 insertions, 163 deletions

diff --git a/include/o3tl/array_view.hxx b/include/o3tl/array_view.hxx
deleted file mode 100644
index dd6ca7fa94c0..000000000000
--- a/include/o3tl/array_view.hxx
+++ /dev/null
@@ -1,163 +0,0 @@
-/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
-/*
- * This file is part of the LibreOffice project.
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/.
- */
-
-#ifndef INCLUDED_O3TL_ARRAY_VIEW_HXX
-#define INCLUDED_O3TL_ARRAY_VIEW_HXX
-
-#include <sal/config.h>
-
-#include <algorithm>
-#include <cstddef>
-#include <ios>
-#include <iterator>
-#include <ostream>
-#include <stdexcept>
-#include <string>
-#include <type_traits>
-#include <utility>
-
-#include <rtl/string.hxx>
-#include <rtl/ustring.hxx>
-#include <sal/types.h>
-
-namespace o3tl {
-
-#if defined _MSC_VER
-#pragma warning(push)
-#pragma warning(disable: 4522) // multiple assignment operators specified
-#endif
-
-/** A barebones approximation of C++17(?) <array_view>.
-  Haven't bothered with more than single-dimensional arrays.
-*/
-template<typename T>
-class array_view {
-    friend class array_view<T const>;
-public:
-    using value_type = T;
-    using pointer = value_type *;
-    using const_pointer = value_type const *;
-    using reference = value_type &;
-    using const_reference = value_type const &;
-    using const_iterator = const_pointer;
-    using iterator = pointer;
-    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
-    using reverse_iterator = std::reverse_iterator<iterator>;
-    using size_type = std::size_t;
-    using difference_type = std::ptrdiff_t;
-
-    static constexpr size_type npos = size_type(-1);
-
-    constexpr array_view() noexcept : data_(nullptr), size_(0) {}
-
-    template<size_type N>
-    constexpr array_view (T (&a)[N]) noexcept : data_(a), size_(N) {}
-
-    constexpr array_view (T *a, size_type len) noexcept
-        : data_(a), size_(len)
-    {
-        // not terribly sure about this, might need to relax it
-        assert((a == nullptr && len == 0) || (a != nullptr && len > 0));
-    }
-
-    /// Allow for assigning array_view<T> to array_view<T const> i.e.
-    ///   array_view<T> a;
-    ///   array_view<T const> b = a;
-    template<typename = std::enable_if< std::is_const<value_type>::value > >
-    array_view& operator=(array_view<typename std::remove_const<value_type>::type> const & other)
-    {
-        data_ = other.data_;
-        size_ = other.size_;
-        return *this;
-    }
-
-    constexpr bool empty() const noexcept { return size_ == 0; }
-
-    constexpr iterator begin() const noexcept { return data_; }
-    constexpr iterator end() const noexcept { return begin() + size(); }
-
-    constexpr const_iterator cbegin() const noexcept { return begin(); }
-    constexpr const_iterator cend() const noexcept { return end(); }
-
-    reverse_iterator rbegin() const noexcept
-    { return reverse_iterator(end()); }
-    reverse_iterator rend() const noexcept
-    { return reverse_iterator(begin()); }
-
-    constexpr const_reverse_iterator crbegin() const noexcept
-    { return rbegin(); }
-    constexpr const_reverse_iterator crend() const noexcept { return rend(); }
-
-    constexpr size_type size() const noexcept { return size_; }
-    constexpr size_type length() const noexcept { return size(); }
-
-    constexpr size_type max_size() const noexcept {
-        (void) this; // silence loplugin:staticmethods
-        return npos - 1;
-    }
-
-    constexpr reference operator [](size_type pos) const {
-        assert(pos < size());
-        return data_[pos];
-    }
-
-    constexpr reference at(size_type pos) const {
-        if (pos >= size()) {
-            throw std::out_of_range("o3tl::array_view::at");
-        }
-        return operator [](pos);
-    }
-
-    constexpr reference front() const {
-        assert(!empty());
-        return operator [](0);
-    }
-
-    constexpr reference back() const {
-        assert(!empty());
-        return operator [](size() - 1);
-    }
-
-    constexpr pointer data() const noexcept { return data_; }
-
-    constexpr void swap(array_view & s) noexcept {
-        std::swap(data_, s.data_);
-        std::swap(size_, s.size_);
-    }
-
-    /// so we can use it in associative containers
-    constexpr bool operator<(array_view const & other) const noexcept {
-        return data_ < other.data_ && size_ < other.size_;
-    }
-
-private:
-    pointer    data_;
-    size_type  size_;
-};
-
-
-#if defined _MSC_VER
-#pragma warning(pop)
-#endif
-
-} // namespace o3tl
-
-namespace std {
-
-template<typename T>
-struct hash<o3tl::array_view<T>> {
-    std::size_t operator()(o3tl::array_view<T> s) const
-    { return hash<T[]>()(s.data(), s.size()); }
-};
-
-} // namespace std
-
-#endif
-
-/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/include/o3tl/span.hxx b/include/o3tl/span.hxx
new file mode 100644
index 000000000000..acb31bab728d
--- /dev/null
+++ b/include/o3tl/span.hxx
@@ -0,0 +1,95 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef INCLUDED_O3TL_SPAN_HXX
+#define INCLUDED_O3TL_SPAN_HXX
+
+#include <sal/config.h>
+
+#if __has_include(<span>)
+
+#include <span>
+
+namespace o3tl { using std::span; }
+
+#else
+
+#include <cassert>
+#include <cstddef>
+#include <iterator>
+
+namespace o3tl {
+
+/** A barebones approximation of C++20 <span>.
+*/
+template<typename T>
+class span {
+public:
+    using value_type = T;
+    using pointer = value_type *;
+    using const_pointer = value_type const *;
+    using reference = value_type &;
+    using const_reference = value_type const &;
+    using const_iterator = const_pointer;
+    using iterator = pointer;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+    using reverse_iterator = std::reverse_iterator<iterator>;
+    using index_type = std::ptrdiff_t;
+    using difference_type = std::ptrdiff_t;
+
+    constexpr span() noexcept : data_(nullptr), size_(0) {}
+
+    template<std::size_t N>
+    constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}
+
+    constexpr span (T *a, index_type len) noexcept
+        : data_(a), size_(len)
+    {
+        // not terribly sure about this, might need to strengthen it
+        assert((a == nullptr && len == 0) || (a != nullptr && len >= 0));
+    }
+
+    constexpr bool empty() const noexcept { return size_ == 0; }
+
+    constexpr iterator begin() const noexcept { return data_; }
+    constexpr iterator end() const noexcept { return begin() + size(); }
+
+    constexpr const_iterator cbegin() const noexcept { return begin(); }
+    constexpr const_iterator cend() const noexcept { return end(); }
+
+    reverse_iterator rbegin() const noexcept
+    { return reverse_iterator(end()); }
+    reverse_iterator rend() const noexcept
+    { return reverse_iterator(begin()); }
+
+    constexpr const_reverse_iterator crbegin() const noexcept
+    { return rbegin(); }
+    constexpr const_reverse_iterator crend() const noexcept { return rend(); }
+
+    constexpr index_type size() const noexcept { return size_; }
+
+    constexpr reference operator [](index_type pos) const {
+        assert(0 <= pos && pos < size());
+        return data_[pos];
+    }
+
+    constexpr pointer data() const noexcept { return data_; }
+
+private:
+    pointer    data_;
+    index_type size_;
+};
+
+} // namespace o3tl
+
+#endif
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */