persist_view.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 <algorithm>
#include <concepts>
#include <memory>
#include <ranges>
 
#include <seqan3/core/detail/iterator_traits.hpp>
#include <seqan3/core/range/detail/adaptor_base.hpp>
#include <seqan3/core/range/type_traits.hpp>
#include <seqan3/utility/range/concept.hpp>
#include <seqan3/utility/type_traits/detail/transformation_trait_or.hpp>
 
namespace seqan3::detail
{
 
// ============================================================================
//  view_persist
// ============================================================================
 
template <std::ranges::input_range urng_t>
class view_persist : public std::ranges::view_interface<view_persist<urng_t>>
{
private:
    std::shared_ptr<urng_t> urange;
 
public:
    view_persist() noexcept = default;                                               
    constexpr view_persist(view_persist const & rhs) noexcept = default;             
    constexpr view_persist(view_persist && rhs) noexcept = default;                  
    constexpr view_persist & operator=(view_persist const & rhs) noexcept = default; 
    constexpr view_persist & operator=(view_persist && rhs) noexcept = default;      
    ~view_persist() noexcept = default;                                              
 
    view_persist(urng_t && _urange) : urange{new urng_t{std::move(_urange)}}
    {}
 
    auto begin() noexcept
    {
        return std::ranges::begin(*urange);
    }
 
    auto begin() const noexcept
        requires const_iterable_range<urng_t>
    {
        return std::ranges::cbegin(*urange);
    }
 
    auto end() noexcept
    {
        return std::ranges::end(*urange);
    }
 
    auto end() const noexcept
        requires const_iterable_range<urng_t>
    {
        return std::ranges::cend(*urange);
    }
};
 
template <typename urng_t>
view_persist(urng_t &&) -> view_persist<std::remove_reference_t<urng_t>>;
 
// ============================================================================
//  persist_fn (adaptor definition)
// ============================================================================
 
 
class persist_fn : public adaptor_base<persist_fn>
{
private:
    using base_t = adaptor_base<persist_fn>;
 
public:
    using base_t::base_t;
 
private:
    friend base_t;
 
    template <std::ranges::viewable_range urng_t>
    static auto impl(urng_t && urange)
    {
        return std::views::all(std::forward<urng_t>(urange));
    }
 
    template <std::ranges::range urng_t>
    static auto impl(urng_t && urange)
    {
        static_assert(!std::is_lvalue_reference_v<urng_t>, "BUG: lvalue-reference in persist_fn::impl().");
        return view_persist{std::move(urange)};
    }
};
 
// ============================================================================
//  detail::persist (adaptor instance definition)
// ============================================================================
 
inline constexpr auto persist = persist_fn{};
 
} // namespace seqan3::detail