single_pass_input.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2022, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2022, Knut Reinert & MPI für molekulare Genetik
// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
// -----------------------------------------------------------------------------------------------------
 
#pragma once
 
#include <cassert>
#include <concepts>
#include <iterator>
#include <memory>
#include <ranges>
#include <type_traits>
 
#include <seqan3/core/detail/iterator_traits.hpp>
#include <seqan3/core/range/detail/adaptor_for_view_without_args.hpp>
 
//-----------------------------------------------------------------------------
// Implementation of single pass input view.
//-----------------------------------------------------------------------------
 
namespace seqan3::detail
{
 
template <typename view_t>
class basic_iterator;
 
template <std::ranges::view urng_t>
class single_pass_input_view : public std::ranges::view_interface<single_pass_input_view<urng_t>>
{
 
private:
    using urng_iterator_type = std::ranges::iterator_t<urng_t>;
 
    template <typename view_t>
    friend class basic_iterator;
 
    struct state
    {
        urng_t urng;
        urng_iterator_type cached_urng_iter = std::ranges::begin(urng);
    };
 
    std::shared_ptr<state> state_ptr{};
 
    using iterator = basic_iterator<single_pass_input_view>;
    using sentinel = std::ranges::sentinel_t<urng_t>;
    //\}
 
public:
    constexpr single_pass_input_view() = default;
    constexpr single_pass_input_view(single_pass_input_view const &) = default;
    constexpr single_pass_input_view(single_pass_input_view &&) = default;
    constexpr single_pass_input_view & operator=(single_pass_input_view const &) = default;
    constexpr single_pass_input_view & operator=(single_pass_input_view &&) = default;
    ~single_pass_input_view() = default;
 
    explicit constexpr single_pass_input_view(urng_t _urng) : state_ptr{new state{std::move(_urng)}}
    {}
 
    template <typename other_urng_t>
        requires (!std::same_as<std::remove_cvref_t<other_urng_t>, single_pass_input_view>
                  && std::ranges::viewable_range<other_urng_t>
                  && // Must come after self type check to avoid conflicts with the move constructor.
                  std::constructible_from<urng_t, std::ranges::ref_view<std::remove_reference_t<other_urng_t>>>)
    explicit constexpr single_pass_input_view(other_urng_t && _urng) : single_pass_input_view{std::views::all(_urng)}
    {}
 
    iterator begin()
    {
        return {*this};
    }
 
    iterator begin() const = delete;
 
    sentinel end()
    {
        return {std::ranges::end(state_ptr->urng)};
    }
 
    sentinel end() const = delete;
};
 
template <std::ranges::viewable_range urng_t>
single_pass_input_view(urng_t &&) -> single_pass_input_view<std::views::all_t<urng_t>>;
} // namespace seqan3::detail
 
//-----------------------------------------------------------------------------
// Iterator for single pass input view.
//-----------------------------------------------------------------------------
 
namespace seqan3::detail
{
template <typename view_type>
class basic_iterator<single_pass_input_view<view_type>>
{
    using base_iterator_type = typename single_pass_input_view<view_type>::urng_iterator_type;
    using sentinel_type = typename single_pass_input_view<view_type>::sentinel;
 
    single_pass_input_view<view_type> * view_ptr{};
 
    template <typename input_view_type>
    friend class basic_iterator;
 
    static_assert(std::sentinel_for<sentinel_type, base_iterator_type>);
 
public:
    using difference_type = std::iter_difference_t<base_iterator_type>;
    using value_type = std::iter_value_t<base_iterator_type>;
    using pointer = detail::iter_pointer_t<base_iterator_type>;
    using reference = std::iter_reference_t<base_iterator_type>;
    using iterator_category = std::input_iterator_tag;
 
    basic_iterator() = default;
    constexpr basic_iterator(basic_iterator const & rhs) = default;
    constexpr basic_iterator(basic_iterator && rhs) = default;
    constexpr basic_iterator & operator=(basic_iterator const & rhs) = default;
    constexpr basic_iterator & operator=(basic_iterator && rhs) = default;
    ~basic_iterator() = default;
 
    basic_iterator(single_pass_input_view<view_type> & view) noexcept : view_ptr{&view}
    {}
 
    reference operator*() const noexcept
    {
        return *cached();
    }
 
    pointer operator->() const noexcept
        requires (!std::is_void_v<pointer>)
    {
        return std::addressof(*cached());
    }
 
    basic_iterator & operator++() noexcept
    {
        ++cached();
        return *this;
    }
 
    void operator++(int) noexcept
    {
        // this post-increment can't be an std::output_iterator, because it would require that `*it++ = value` must have
        // the same semantic as `*i = value; ++i`, but it actually has the following `++i; *i = value` semantic, due to
        // the centralised storage of the underlying_iterator in the view where each copy of a basic_iterator points to
        // the same centralised state.
        ++(*this);
    }
 
    constexpr bool operator==(sentinel_type const & s) const noexcept
    {
        return cached() == s;
    }
 
    friend constexpr bool operator==(sentinel_type const & s, basic_iterator const & rhs) noexcept
    {
        return rhs == s;
    }
 
    constexpr bool operator!=(sentinel_type const & rhs) const noexcept
    {
        return !(*this == rhs);
    }
 
    friend constexpr bool operator!=(sentinel_type const & s, basic_iterator const & rhs) noexcept
    {
        return rhs != s;
    }
 
protected:
    base_iterator_type & cached() const noexcept
    {
        assert(view_ptr != nullptr);
        assert(view_ptr->state_ptr != nullptr);
        return view_ptr->state_ptr->cached_urng_iter;
    }
};
} // namespace seqan3::detail
 
//-----------------------------------------------------------------------------
// View shortcut for functor.
//-----------------------------------------------------------------------------
 
namespace seqan3::views
{
inline constexpr auto single_pass_input = detail::adaptor_for_view_without_args<detail::single_pass_input_view>{};
 
} // namespace seqan3::views