combine_latest.hpp

//                   ReactivePlusPlus library
//
//           Copyright Aleksey Loginov 2022 - present.
//                             TC Wang 2022 - present.
//  Distributed under the Boost Software License, Version 1.0.
//     (See accompanying file LICENSE_1_0.txt or copy at
//           https://www.boost.org/LICENSE_1_0.txt)
//
//  Project home: https://github.com/victimsnino/ReactivePlusPlus
 
#pragma once
 
#include <rpp/observables/constraints.hpp>              // constraint::observable
#include <rpp/observables/details/member_overload.hpp>  // member_overload
#include <rpp/utils/function_traits.hpp>                // decayed_invoke_result_t
#include <rpp/utils/functors.hpp>                       // pack_to_tuple
 
#include <tuple>
 
namespace rpp::details
{
struct combine_latest_tag;
}
 
namespace rpp::details
{
 
template<constraint::decayed_type Type, typename TCombiner, constraint::observable ...TOtherObservable>
struct combine_latest_impl;
 
template<constraint::decayed_type Type, typename SpecificObservable>
struct member_overload<Type, SpecificObservable, combine_latest_tag>
{
 
    template<constraint::observable ...TOtherObservable, std::invocable<Type, utils::extract_observable_type_t<TOtherObservable>...> TCombiner>
    auto combine_latest(TCombiner&& combiner, TOtherObservable&&...observables) const& requires is_header_included<combine_latest_tag, TOtherObservable...>
    {
        using DownstreamType = utils::decayed_invoke_result_t<TCombiner, Type, utils::extract_observable_type_t<TOtherObservable>...>;
 
        return cast_this()->template lift<DownstreamType>(
            combine_latest_impl<Type, std::decay_t<TCombiner>, std::decay_t<TOtherObservable>...>{
                std::forward<TCombiner>(combiner),
                std::tuple{std::forward<TOtherObservable>(observables)...}
            });
    }
 
    template<constraint::observable ...TOtherObservable, std::invocable<Type, utils::extract_observable_type_t<TOtherObservable>...> TCombiner>
    auto combine_latest(TCombiner&& combiner, TOtherObservable&&...observables) && requires is_header_included<combine_latest_tag, TOtherObservable...>
    {
        using DownstreamType = utils::decayed_invoke_result_t<TCombiner, Type, utils::extract_observable_type_t<TOtherObservable>...>;
 
        return move_this().template lift<DownstreamType>(
            combine_latest_impl<Type, std::decay_t<TCombiner>, std::decay_t<TOtherObservable>...>{
                std::forward<TCombiner>(combiner),
                std::tuple{std::forward<TOtherObservable>(observables)...}
            });
    }
 
    template<constraint::observable ...TOtherObservable>
    auto combine_latest(TOtherObservable&&...observables) const& requires is_header_included<combine_latest_tag, TOtherObservable...>
    {
        return cast_this()->combine_latest(utils::pack_to_tuple{}, std::forward<TOtherObservable>(observables)...);
    }
 
    template<constraint::observable ...TOtherObservable>
    auto combine_latest(TOtherObservable&&...observables) && requires is_header_included<combine_latest_tag, TOtherObservable...>
    {
        return move_this().combine_latest(utils::pack_to_tuple{}, std::forward<TOtherObservable>(observables)...);
    }
 
private:
    const SpecificObservable* cast_this() const
    {
        return static_cast<const SpecificObservable*>(this);
    }
 
    SpecificObservable&& move_this()
    {
        return std::move(*static_cast<SpecificObservable*>(this));
    }
};
 
} // namespace rpp::details