flat_map.hpp

//                  ReactivePlusPlus library
//
//          Copyright Aleksey Loginov 2023 - 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/AlexInLog/ReactivePlusPlus
//
 
#pragma once
 
#include <rpp/defs.hpp>
#include <rpp/operators/map.hpp>
#include <rpp/operators/merge.hpp>
 
namespace rpp::operators::details
{
    template<rpp::constraint::decayed_type Fn>
    struct flat_map_t
    {
        RPP_NO_UNIQUE_ADDRESS Fn m_fn;
 
        template<rpp::constraint::observable TObservable>
        auto operator()(TObservable&& observable) const &
        {
            static_assert(std::invocable<Fn, rpp::utils::extract_observable_type_t<TObservable>> && rpp::constraint::observable<std::invoke_result_t<Fn, rpp::utils::extract_observable_type_t<TObservable>>>, "fn should return observable");
            return std::forward<TObservable>(observable)
                 | rpp::ops::map(m_fn)
                 | rpp::ops::merge();
        }
 
        template<rpp::constraint::observable TObservable>
        auto operator()(TObservable&& observable) &&
        {
            static_assert(std::invocable<Fn, rpp::utils::extract_observable_type_t<TObservable>> && rpp::constraint::observable<std::invoke_result_t<Fn, rpp::utils::extract_observable_type_t<TObservable>>>, "fn should return observable");
            return std::forward<TObservable>(observable)
                 | rpp::ops::map(std::move(m_fn))
                 | rpp::ops::merge();
        }
    };
 
} // namespace rpp::operators::details
 
namespace rpp::operators
{

     * @see https://reactivex.io/documentation/operators/flatmap.html
     */
    template<typename Fn>
        requires (!utils::is_not_template_callable<Fn> || rpp::constraint::observable<std::invoke_result_t<Fn, rpp::utils::convertible_to_any>>)
    auto flat_map(Fn&& callable)
    {
        return details::flat_map_t<std::decay_t<Fn>>{std::forward<Fn>(callable)};
    }
 
} // namespace rpp::operators