random_access_iterator.hpp

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// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause
 
#pragma once
 
#include <cassert>
#include <iterator>
#include <type_traits>
 
#include <seqan3/core/platform.hpp>
 
namespace seqan3::detail
{
 
template <typename range_type, template <typename...> typename derived_t_template, typename... args_t>
class random_access_iterator_base
{
protected:
    typename std::add_pointer_t<range_type> host{nullptr};
    using position_type = std::make_unsigned_t<typename range_type::difference_type>;
    position_type pos{static_cast<position_type>(0)};
 
    template <typename range_type2, template <typename...> typename derived_t_template2, typename... args2_t>
    friend class random_access_iterator_base;
 
    using derived_t = derived_t_template<range_type>;
 
public:
    using difference_type = typename range_type::difference_type; // TODO should be range_ but is broken in ranges
    using value_type = typename range_type::value_type;
    using reference = std::conditional_t<std::is_const_v<range_type>,
                                         typename range_type::const_reference,
                                         typename range_type::reference>;
    using const_reference = typename range_type::const_reference; //TODO: there is no type trait for this, yet :o
    using pointer = value_type *;
    using iterator_category = std::random_access_iterator_tag;
 
    constexpr random_access_iterator_base() = default;
    constexpr random_access_iterator_base(random_access_iterator_base const &) = default;
    constexpr random_access_iterator_base & operator=(random_access_iterator_base const &) = default;
    constexpr random_access_iterator_base(random_access_iterator_base &&) = default;
    constexpr random_access_iterator_base & operator=(random_access_iterator_base &&) = default;
    ~random_access_iterator_base() = default;
 
    explicit constexpr random_access_iterator_base(range_type & host) noexcept : host{&host}
    {}
    constexpr random_access_iterator_base(range_type & host, position_type const pos) noexcept : host{&host}, pos{pos}
    {}
 
    template <typename range_type2>
        requires std::is_const_v<range_type> && (!std::is_const_v<range_type2>)
                  && std::is_same_v<std::remove_const_t<range_type>, range_type2>
    constexpr random_access_iterator_base(
        random_access_iterator_base<range_type2, derived_t_template> const & rhs) noexcept :
        host{rhs.host},
        pos{rhs.pos}
    {}
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator==(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return pos == rhs.pos;
    }
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator!=(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return !(*this == rhs);
    }
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator<(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return static_cast<bool>(pos < rhs.pos);
    }
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator>(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return pos > rhs.pos;
    }
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator<=(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return pos <= rhs.pos;
    }
 
    template <typename range_type2>
        requires std::is_same_v<std::remove_const_t<range_type>, std::remove_const_t<range_type2>>
    constexpr bool operator>=(random_access_iterator_base<range_type2, derived_t_template> const & rhs) const noexcept
    {
        return pos >= rhs.pos;
    }
 
    constexpr derived_t & operator++() noexcept
    {
        ++pos;
        return *this_derived();
    }
 
    constexpr derived_t operator++(int) noexcept
    {
        derived_t cpy{*this_derived()};
        ++pos;
        return cpy;
    }
 
    constexpr derived_t & operator--() noexcept
    {
        --pos;
        return *this_derived();
    }
 
    constexpr derived_t operator--(int) noexcept
    {
        derived_t cpy{*this_derived()};
        --pos;
        return cpy;
    }
 
    constexpr derived_t & operator+=(difference_type const skip) noexcept
    {
        pos += skip;
        return *this_derived();
    }
 
    constexpr derived_t operator+(difference_type const skip) const noexcept
    {
        derived_t cpy{*this_derived()};
        return cpy += skip;
    }
 
    constexpr friend derived_t operator+(difference_type const skip, derived_t const & it) noexcept
    {
        return it + skip;
    }
 
    constexpr derived_t & operator-=(difference_type const skip) noexcept
    {
        pos -= skip;
        return *this_derived();
    }
 
    constexpr derived_t operator-(difference_type const skip) const noexcept
    {
        derived_t cpy{*this_derived()};
        return cpy -= skip;
    }
 
    constexpr friend derived_t operator-(difference_type const skip, derived_t const & it) noexcept
    {
        return it - skip;
    }
 
    constexpr friend difference_type operator-(derived_t const & lhs, derived_t const & rhs) noexcept
    {
        return static_cast<difference_type>(lhs.pos - rhs.pos);
    }
 
    constexpr reference operator*() const noexcept(noexcept((*host)[pos]))
    {
        return (*host)[pos];
    }
 
    constexpr pointer operator->() const noexcept(noexcept((&host)[pos]))
    {
        return &host[pos];
    }
 
    constexpr reference operator[](position_type const n) const noexcept(noexcept((*host)[pos + n]))
    {
        return (*host)[pos + n];
    }
 
private:
    constexpr derived_t * this_derived()
    {
        return static_cast<derived_t *>(this);
    }
 
    constexpr derived_t const * this_derived() const
    {
        return static_cast<derived_t const *>(this);
    }
};
 
template <typename range_type>
class random_access_iterator : public random_access_iterator_base<range_type, random_access_iterator>
{
private:
    using base = random_access_iterator_base<range_type, random_access_iterator>;
    using typename base::position_type;
 
public:
    using typename base::const_reference;
    using typename base::difference_type;
    using typename base::iterator_category;
    using typename base::pointer;
    using typename base::reference;
    using typename base::value_type;
 
    using base::base;
};
 
} // namespace seqan3::detail