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https://github.com/boostorg/stl_interfaces.git
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Break take_view out into its own header, in example/.
This commit is contained in:
Zach Laine
141
example/take_view.hpp
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141
example/take_view.hpp
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// Copyright (C) 2022 T. Zachary Laine
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_STL_INTERFACES_EXAMPLE_TAKE_VIEW_HPP
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#define BOOST_STL_INTERFACES_EXAMPLE_TAKE_VIEW_HPP
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#include "all_view.hpp"
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namespace detail {
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//[ take_view_defn
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// This is a really simple iterator that converts the given iterator Iter
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// to a forward_iterator that counts how many times it has ben
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// incremented. It counts down from an initial count to zero.
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template<typename Iter>
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struct take_iterator
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: boost::stl_interfaces::iterator_interface<
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take_iterator<Iter>,
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std::forward_iterator_tag,
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typename std::iterator_traits<Iter>::value_type,
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typename std::iterator_traits<Iter>::reference,
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typename std::iterator_traits<Iter>::pointer,
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typename std::iterator_traits<Iter>::difference_type>
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{
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constexpr take_iterator() = default;
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constexpr explicit take_iterator(Iter it, int n) :
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it_(std::move(it)), n_(n)
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{}
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constexpr Iter base() const { return it_; }
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constexpr int count() const { return n_; }
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constexpr take_iterator & operator++()
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{
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++it_;
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--n_;
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return *this;
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}
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private:
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friend boost::stl_interfaces::access;
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constexpr Iter & base_reference() { return it_; }
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constexpr Iter const & base_reference() const { return it_; }
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template<typename Iter2>
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friend struct take_iterator;
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Iter it_;
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int n_;
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};
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// This sentinel compares equal to any take_iterator whose count has
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// reached zero.
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template<typename Sentinel>
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struct take_sentinel
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{
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take_sentinel() = default;
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explicit take_sentinel(Sentinel sent) : sent_(sent) {}
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template<typename Iter>
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friend constexpr bool
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operator==(take_iterator<Iter> it, take_sentinel s)
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{
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return !it.count() || it.base() == s.sent_;
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}
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template<typename Iter>
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friend constexpr bool
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operator!=(take_iterator<Iter> it, take_sentinel s)
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{
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return !(it == s);
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}
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private:
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Sentinel sent_;
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};
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// The take_iterator and take_sentinel templates do all the hard work,
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// which keeps take_view quie simple.
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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template<std::ranges::view View>
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requires std::is_object_v<View>
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#else
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template<
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typename View,
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typename Enable = std::enable_if_t<std::is_object<View>::value>>
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#endif
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struct take_view : boost::stl_interfaces::view_interface<take_view<View>>
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{
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using iterator = take_iterator<iterator_t<View>>;
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using sentinel = take_sentinel<sentinel_t<View>>;
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// We don't need a phony initial int param for this constructor, since
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// it already takes two parameters; it won't get confused for a copy
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// or a move. The count here is just an int to keep things simple.
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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template<typename View2>
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requires std::is_same_v<std::remove_reference_t<View2>, View>
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#else
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template<
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typename View2,
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typename E = std::enable_if_t<
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std::is_same<std::remove_reference_t<View2>, View>::value>>
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#endif
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explicit take_view(View2 && r, int n) :
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first_(r.begin(), n), last_(r.end())
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{}
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iterator begin() const { return first_; }
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sentinel end() const { return last_; }
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private:
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iterator first_;
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sentinel last_;
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};
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// This just makes out implementations below a bit easier to write.
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#if defined(__cpp_deduction_guides)
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template<typename R>
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take_view(R &&, int)->detail::take_view<std::remove_reference_t<R>>;
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#endif
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//]
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}
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#if defined(__cpp_deduction_guides)
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//[ take_defn
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// Use the adaptor template to support calling the given lambda with either
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// all the parameters or all the parameters after the first.
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inline constexpr boost::stl_interfaces::adaptor take =
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[]<typename R>(R && r, int n) { return detail::take_view((R &&) r, n); };
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//]
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#endif
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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namespace std::ranges {
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template<typename View>
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inline constexpr bool enable_borrowed_range<detail::take_view<View>> = true;
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}
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#endif
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#endif
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@@ -10,6 +10,7 @@
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#include "ill_formed.hpp"
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#include "../example/all_view.hpp"
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#include "../example/reverse_view.hpp"
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#include "../example/take_view.hpp"
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#include <boost/core/lightweight_test.hpp>
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@@ -17,178 +18,61 @@
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#include <vector>
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namespace detail {
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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template<std::ranges::view View>
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requires std::is_object_v<View>
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#else
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template<
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typename View,
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typename Enable = std::enable_if_t<std::is_object<View>::value>>
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#endif
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struct take_view
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: boost::stl_interfaces::view_interface<take_view<View>>
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namespace detail {
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template<
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typename R,
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bool ReverseView = is_reverse_view<std::decay_t<R>>::value>
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struct reverse_impl_impl
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{
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static constexpr auto call(R && r) { return ((R &&) r).base(); }
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};
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template<typename R>
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struct reverse_impl_impl<R, false>
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{
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static constexpr auto call(R && r)
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{
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template<typename Iter>
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struct counted_iterator
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: boost::stl_interfaces::iterator_interface<
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counted_iterator<Iter>,
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std::forward_iterator_tag,
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typename std::iterator_traits<Iter>::value_type,
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typename std::iterator_traits<Iter>::reference,
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typename std::iterator_traits<Iter>::pointer,
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typename std::iterator_traits<Iter>::difference_type>
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{
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constexpr counted_iterator() = default;
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constexpr explicit counted_iterator(Iter it, int n) :
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it_(std::move(it)), n_(n)
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{}
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return reverse_view<std::remove_reference_t<R>>(0, (R &&) r);
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}
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};
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constexpr Iter base() const { return it_; }
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constexpr int count() const { return n_; }
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constexpr counted_iterator & operator++()
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{
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++it_;
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--n_;
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return *this;
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}
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private:
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friend boost::stl_interfaces::access;
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constexpr Iter & base_reference() { return it_; }
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constexpr Iter const & base_reference() const { return it_; }
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template<typename Iter2>
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friend struct counted_iterator;
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Iter it_;
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int n_;
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};
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template<typename Sentinel>
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struct counted_sentinel
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{
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counted_sentinel() = default;
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explicit counted_sentinel(Sentinel sent) : sent_(sent) {}
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template<typename Iter>
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friend constexpr bool
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operator==(counted_iterator<Iter> it, counted_sentinel s)
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{
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return !it.count() || it.base() == s.sent_;
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}
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template<typename Iter>
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friend constexpr bool
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operator!=(counted_iterator<Iter> it, counted_sentinel s)
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{
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return !(it == s);
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}
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private:
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Sentinel sent_;
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};
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using iterator = counted_iterator<iterator_t<View>>;
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using sentinel = counted_sentinel<sentinel_t<View>>;
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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template<typename View2>
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requires std::is_same_v<std::remove_reference_t<View2>, View>
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#else
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template<
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typename View2,
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typename E = std::enable_if_t<
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std::is_same<std::remove_reference_t<View2>, View>::value>>
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#endif
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explicit take_view(View2 && r, int n) :
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first_(r.begin(), n), last_(r.end())
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{}
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iterator begin() const { return first_; }
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sentinel end() const { return last_; }
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private:
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iterator first_;
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sentinel last_;
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};
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struct take_impl
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{
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template<typename R>
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constexpr auto operator()(R && r, int n) const
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{
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return take_view<std::remove_reference_t<R>>((R &&) r, n);
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}
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constexpr auto operator()(int n) const
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{
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using closure_func_type =
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decltype(boost::stl_interfaces::bind_back(*this, n));
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return boost::stl_interfaces::closure<closure_func_type>(
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boost::stl_interfaces::bind_back(*this, n));
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}
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};
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template<
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typename R,
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bool ReverseView = is_reverse_view<std::decay_t<R>>::value>
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struct reverse_impl_impl
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{
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static constexpr auto call(R && r) { return ((R &&) r).base(); }
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};
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struct reverse_impl
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: boost::stl_interfaces::range_adaptor_closure<reverse_impl>
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{
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template<typename R>
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struct reverse_impl_impl<R, false>
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constexpr auto operator()(R && r) const
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{
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static constexpr auto call(R && r)
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{
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return reverse_view<std::remove_reference_t<R>>(0, (R &&) r);
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}
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};
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return reverse_impl_impl<R>::call((R &&) r);
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}
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};
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struct reverse_impl
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: boost::stl_interfaces::range_adaptor_closure<reverse_impl>
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struct take_impl
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{
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template<typename R>
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constexpr auto operator()(R && r, int n) const
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{
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template<typename R>
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constexpr auto operator()(R && r) const
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{
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return reverse_impl_impl<R>::call((R &&) r);
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}
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};
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}
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return take_view<std::remove_reference_t<R>>((R &&) r, n);
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}
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#if BOOST_STL_INTERFACES_USE_CONCEPTS
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namespace std::ranges {
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template<typename View>
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inline constexpr bool enable_borrowed_range<detail::take_view<View>> = true;
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constexpr auto operator()(int n) const
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{
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using closure_func_type =
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decltype(boost::stl_interfaces::bind_back(*this, n));
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return boost::stl_interfaces::closure<closure_func_type>(
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boost::stl_interfaces::bind_back(*this, n));
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}
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};
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}
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#endif
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#if defined(__cpp_inline_variables)
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inline constexpr detail::reverse_impl old_reverse;
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#else
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namespace {
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constexpr detail::reverse_impl old_reverse;
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}
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#endif
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#if defined(__cpp_inline_variables)
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inline constexpr detail::take_impl old_take;
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#else
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namespace {
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constexpr detail::reverse_impl old_reverse;
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constexpr detail::take_impl old_take;
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}
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#endif
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#if 201703L <= __cplusplus
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inline constexpr boost::stl_interfaces::adaptor take =
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[]<typename R>(R && r, int n) {
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return detail::take_view<std::remove_reference_t<R>>((R &&) r, n);
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};
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#endif
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int main()
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{
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// non-closures
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