deep.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2020, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2020, 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 <seqan3/range/views/detail.hpp>
#include <seqan3/std/ranges>
 
namespace seqan3::views
{
 
template <typename underlying_adaptor_t>
class deep : public detail::adaptor_base<deep<underlying_adaptor_t>, underlying_adaptor_t>
{
private:
    using base_type = detail::adaptor_base<deep<underlying_adaptor_t>, underlying_adaptor_t>;
 
    friend base_type;
 
public:
    constexpr deep()                         noexcept = default; 
    constexpr deep(deep const &)             noexcept = default; 
    constexpr deep(deep &&)                  noexcept = default; 
    constexpr deep & operator=(deep const &) noexcept = default; 
    constexpr deep & operator=(deep &&)      noexcept = default; 
    ~deep()                                  noexcept = default; 
 
    using base_type::base_type;
 
 
    using base_type::operator();
 
    template <std::ranges::input_range urng_t, typename underlying_adaptor_t_>
    static constexpr auto impl(urng_t && urange, underlying_adaptor_t_ && deep_adaptor)
    {
        static_assert(std::same_as<underlying_adaptor_t_, underlying_adaptor_t>,
                      "Internally stored deep-adaptor does not match!");
 
        constexpr size_t range_dimension = range_dimension_v<urng_t>;
 
        // note: if range_dimension == 1, the expression will actually be
        // `std::forward<underlying_adaptor_t_>(adap)(urange)`, thus allowing the stateful adaptor to move its arguments
        // into the view that will be constructed.
        return recursive_adaptor<range_dimension>(std::forward<underlying_adaptor_t_>(deep_adaptor))(urange);
    }
 
    template <std::size_t range_dimension>
    static constexpr decltype(auto) recursive_adaptor(underlying_adaptor_t deep_adaptor)
    {
        if constexpr (range_dimension > 1u)
        {
            auto transform
                = [adaptor = recursive_adaptor<range_dimension - 1u>(std::forward<underlying_adaptor_t>(deep_adaptor))]
                  (auto && inner_range)
            {
                // We don't want to move a stateful adaptor here, as this adaptor will be called on any element of this
                // std::views::transform range.
                return adaptor(std::forward<decltype(inner_range)>(inner_range));
            };
            return std::views::transform(std::move(transform));
        }
        else
        {
            // recursion anchor: only the innermost std::views::transform will store the deep_adaptor.
            // In an earlier version of seqan3 we recursively passed the deep_adaptor through all std::view::transform
            // instances and each depth stored the same deep_adaptor. The current approach can save memory as it only
            // stores the deep_adaptor once in the innermost std::views::transform. It will also produce slightly better
            // stack-traces by defining the recursion over the range_dimension.
 
            // NOTE: to allow an lvalue to be returned we need to have the return type decltype(auto).
            return deep_adaptor;
        }
    }
 
    template <typename first_arg_t, typename ...stored_arg_types>
        requires (!std::ranges::input_range<first_arg_t>)
    constexpr auto operator()(first_arg_t && first, stored_arg_types && ...args) const
    {
        // The adaptor currently wrapped is a proto-adaptor and this function has the arguments to "complete" it.
        // We extract the adaptor that is stored and invoke it with the given arguments.
        // This returns an adaptor closure object.
        auto adaptor_closure = std::get<0>(this->arguments)(std::forward<first_arg_t>(first),
                                                            std::forward<stored_arg_types>(args)...);
        // Now we wrap this closure object back into a views::deep to get the deep behaviour.
        return deep<decltype(adaptor_closure)>{std::move(adaptor_closure)};
    }
 
    constexpr auto operator()() const
    {
        // Proto-adaptors require arguments by definition, but some support defaulting those (e.g. views::translate).
        // This extracts the proto adaptor and invokes it without args which yields a different object, the closure
        // with default arguments.
        auto adaptor_closure = std::get<0>(this->arguments)();
        // Now we wrap this closure object back into a views::deep to get the deep behaviour.
        return deep<decltype(adaptor_closure)>{std::move(adaptor_closure)};
    }
 
    template <std::ranges::input_range urng_t, typename ...stored_arg_types>
        requires (sizeof...(stored_arg_types) > 0)
    constexpr auto operator()(urng_t && urange, stored_arg_types && ...args) const
    {
        auto adaptor_closure = std::get<0>(this->arguments)(std::forward<stored_arg_types>(args)...);
        deep<decltype(adaptor_closure)> deep_adaptor{std::move(adaptor_closure)};
        return deep_adaptor(std::forward<urng_t>(urange));
    }
};
 
template <typename underlying_adaptor_t>
deep(underlying_adaptor_t && inner) -> deep<underlying_adaptor_t>;
 
 
} // namespace seqan3::views