437 lines
14 KiB
C++
437 lines
14 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2015-2017 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_VIEW_HPP
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#define CRUFT_UTIL_VIEW_HPP
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#include "cast.hpp"
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#include "debug.hpp"
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#include "types/traits.hpp"
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#include <cstdlib>
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#include <ostream>
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#include <string>
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#include <cstring>
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#include <stdexcept>
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#include <iterator>
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namespace util {
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template <typename IteratorA, typename IteratorB = IteratorA>
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struct view {
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public:
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//---------------------------------------------------------------------
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using value_type = typename std::iterator_traits<
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remove_restrict_t<IteratorA>
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>::value_type;
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//---------------------------------------------------------------------
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constexpr
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view (const IteratorA &first, const IteratorB &last) noexcept:
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m_begin (first),
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m_end (last)
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{ ; }
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//---------------------------------------------------------------------
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// explicitly cater for the char array case so that we don't
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// accidentally include the trailing null in the data.
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template <std::size_t N>
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view (const char (&value)[N]):
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view (std::begin (value), std::begin (value) + N - 1)
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{
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static_assert (N > 0);
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}
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//---------------------------------------------------------------------
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template <std::size_t N, typename ValueT>
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view (const ValueT(&value)[N]):
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view (std::begin (value), std::end (value))
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{ ; }
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//---------------------------------------------------------------------
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constexpr
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view (const view &rhs) noexcept:
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view (rhs.m_begin, rhs.m_end)
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{ ; }
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//---------------------------------------------------------------------
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// technically we could get away without explicitly defining a move
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// constructor here, but by nulling rhs we can more easily use this
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// class as a base for unique owning pointers without exposing the
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// begin/end data members to them directly.
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constexpr view (view &&rhs) noexcept:
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view (std::move (rhs.m_begin), std::move (rhs.m_end))
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{ ; }
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//---------------------------------------------------------------------
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// allow null construction of views where IteratorT is constructible
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// from nullptr_t
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//
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// ideally we would avoid exposing this as it promotes use of nulls but
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// it simplifies construction of views that are data members of classes
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// when we may not immediately know the values we should contain.
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constexpr view (std::nullptr_t) noexcept:
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view {nullptr,nullptr}
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{ ; }
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//---------------------------------------------------------------------
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template <typename ContainerT>
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constexpr explicit
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view (ContainerT &klass):
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view (std::begin (klass), std::end (klass))
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{ ; }
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//---------------------------------------------------------------------
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template <typename ContainerT>
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constexpr explicit
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view (const ContainerT &klass):
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view (std::begin (klass), std::end (klass))
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{ ; }
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//---------------------------------------------------------------------
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view&
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operator= (const view &rhs) noexcept
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{
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m_begin = rhs.m_begin;
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m_end = rhs.m_end;
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return *this;
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}
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//---------------------------------------------------------------------
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view&
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operator= (view &&rhs) noexcept
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{
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m_begin = rhs.m_begin;
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m_end = rhs.m_end;
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rhs.m_begin = IteratorA{};
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rhs.m_end = IteratorB{};
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return *this;
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};
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///////////////////////////////////////////////////////////////////////
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constexpr IteratorA begin (void) noexcept { return m_begin; }
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constexpr IteratorB end (void) noexcept { return m_end; }
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//---------------------------------------------------------------------
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constexpr const IteratorA begin (void) const noexcept { return cbegin (); }
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constexpr const IteratorB end (void) const noexcept { return cend (); }
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//---------------------------------------------------------------------
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constexpr const IteratorA cbegin (void) const noexcept { return m_begin; }
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constexpr const IteratorB cend (void) const noexcept { return m_end; }
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//---------------------------------------------------------------------
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auto data (void) { return begin (); }
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auto data (void) const { return begin (); }
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///////////////////////////////////////////////////////////////////////
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constexpr bool
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empty (void) const noexcept
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{
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return m_begin == m_end;
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}
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//---------------------------------------------------------------------
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constexpr auto
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size (void) const noexcept
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{
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return sign_cast<std::size_t> (std::distance (m_begin, m_end));
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}
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//---------------------------------------------------------------------
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[[gnu::warn_unused_result]] constexpr auto
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redim (int count) const
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{
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CHECK_GT (count, 0);
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if (count > size ())
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throw std::invalid_argument ("redim to higher size not allowed");
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return view { m_begin, m_begin + count };
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};
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//---------------------------------------------------------------------
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// returns a view that has the same end iterator, but the provided
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// begin iterator.
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//
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// the new begin iterator must be reachable by incrementing the current
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// begin iterator but lie before reaching the end iterator. ie, in the
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// middle.
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//
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// useful for resizing views after options which incrementally consume
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// the referenced data.
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[[gnu::warn_unused_result]] constexpr auto
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increment (IteratorA _begin) const
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{
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return view { _begin, m_end };
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}
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//---------------------------------------------------------------------
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[[gnu::warn_unused_result]] constexpr auto
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increment (int count) const
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{
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IteratorA next;
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std::advance (next, count);
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return increment (next);
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}
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//---------------------------------------------------------------------
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template <typename IteratorC>
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[[gnu::warn_unused_result]] constexpr auto
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decrement (IteratorC _end)
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{
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return view { m_begin, _end };
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};
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///////////////////////////////////////////////////////////////////////
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constexpr auto&
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operator[] (size_t idx)& noexcept
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{
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auto it = begin ();
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std::advance (it, idx);
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return *it;
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}
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//---------------------------------------------------------------------
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constexpr auto&
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operator[] (size_t idx) const& noexcept
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{
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auto it = begin ();
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std::advance (it, idx);
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return *it;
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}
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private:
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///////////////////////////////////////////////////////////////////////
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IteratorA m_begin;
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IteratorB m_end;
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};
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///////////////////////////////////////////////////////////////////////////
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template <typename ValueT, size_t N>
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auto
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make_view (const ValueT (&arr)[N])
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{
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return util::view<const ValueT*> (arr + 0, arr + N);
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}
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//-------------------------------------------------------------------------
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template <typename ContainerT>
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auto
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make_view (ContainerT &t)
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{
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return util::view<decltype(std::begin (t))> { std::begin (t), std::end (t) };
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}
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//-------------------------------------------------------------------------
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template <typename ContainerT>
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auto
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make_view (const ContainerT &t)
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{
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return util::view<decltype(std::cbegin (t))> { std::cbegin (t), std::cend (t) };
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}
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//-------------------------------------------------------------------------
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// disable the possibility of creating a view to a temporary. note that
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// this only works if an lval version has already been defined otherwise
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// universal reference rules will capture both lval and rval here.
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template <typename ContainerT>
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auto
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make_view (ContainerT&&) = delete;
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///////////////////////////////////////////////////////////////////////////
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template <typename ContainerT>
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auto
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make_cview (const ContainerT &t)
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{
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return util::view<decltype(std::cbegin (t))> { std::cbegin (t), std::cend (t) };
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}
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//-------------------------------------------------------------------------
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template <typename IteratorA, typename IteratorB>
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auto
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make_view (IteratorA first, IteratorB last)
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{
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return view<IteratorA, IteratorB> {first, last};
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}
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//-------------------------------------------------------------------------
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template <typename ValueT>
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auto
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make_cview (ValueT *first, ValueT *last)
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{
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return view<const ValueT*> {first, last};
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}
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///////////////////////////////////////////////////////////////////////////
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inline
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view<const char*> make_view (const char *str)
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{
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return { str, str + strlen (str) };
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}
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//-------------------------------------------------------------------------
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inline
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view<char*> make_view (char *str)
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{
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return { str, str + strlen (str) };
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}
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//-------------------------------------------------------------------------
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template <typename CharT, typename TraitsT, typename AllocT>
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view<const CharT*>
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make_view (const std::basic_string<CharT,TraitsT,AllocT> &str)
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{
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return {
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std::data (str),
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std::data (str) + std::size (str)
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};
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}
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//-------------------------------------------------------------------------
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template <typename CharT, typename TraitsT, typename AllocT>
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view<CharT*>
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make_view (std::basic_string<CharT,TraitsT,AllocT> &str)
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{
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return {
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std::data (str),
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std::data (str) + std::size (str)
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};
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}
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//-------------------------------------------------------------------------
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template <typename CharT, typename TraitsT, typename AllocT>
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view<const CharT*>
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make_view (const std::basic_string<CharT,TraitsT,AllocT>&&) = delete;
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//-------------------------------------------------------------------------
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template <typename CharT, typename TraitsT, typename AllocT>
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view<CharT*>
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make_view (std::basic_string<CharT,TraitsT,AllocT>&&) = delete;
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///////////////////////////////////////////////////////////////////////////
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template <typename IteratorA, typename IteratorB>
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constexpr bool
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operator== (const view<IteratorA> &a, const view<IteratorB> &b)
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{
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return a.size () == b.size () &&
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std::equal (std::begin (a), std::end (a), std::begin (b));
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}
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//-------------------------------------------------------------------------
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// defer equality to the view/view operator by way of make_view
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template <typename IteratorT, typename ValueT>
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constexpr bool
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operator== (const view<IteratorT> &a, const ValueT &b)
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{
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return a == make_view (b);
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}
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//-------------------------------------------------------------------------
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// reverse the arguments and forward to the above operator. we formumlate
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// equality this way to avoid implementing the operator twice for each
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// weird case.
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template <typename IteratorT, typename ValueT>
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constexpr bool
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operator== (const ValueT &a, const view<IteratorT> &b)
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{
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return b == a;
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}
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///////////////////////////////////////////////////////////////////////////
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template <typename IteratorT, typename ValueT>
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constexpr bool
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operator!= (const util::view<IteratorT> &a, const ValueT &b)
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{
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return !(a == b);
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}
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//-------------------------------------------------------------------------
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template <typename IteratorT, typename ValueT>
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constexpr bool
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operator!= (const ValueT &a, const util::view<IteratorT> &b)
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{
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return !(a == b);
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}
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///////////////////////////////////////////////////////////////////////////
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template <typename IteratorT>
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std::ostream&
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operator<< (std::ostream &os, view<IteratorT> val)
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{
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std::copy (
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std::cbegin (val),
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std::cend (val),
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std::ostream_iterator<typename decltype(val)::value_type> (os)
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);
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return os;
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}
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///////////////////////////////////////////////////////////////////////////
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/// a basic stringlike comparison operator that behaves as
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/// std::string::compare would.
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///
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/// provided so that the common case of stringlike views can be used in a
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/// std::map and similar without a great deal of work.
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inline bool
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operator< (util::view<const char*> a, util::view<const char*> b)
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{
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const auto la = std::size (a);
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const auto lb = std::size (b);
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const auto res = strncmp (
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std::data (a),
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std::data (b),
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util::min (la, lb)
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);
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return res < 0 || (res == 0 && la < lb);
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}
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}
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#endif
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