reduce.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/operators/fwd.hpp>
 
#include <rpp/defs.hpp>
#include <rpp/operators/details/strategy.hpp>
 
namespace rpp::operators::details
{
    template<rpp::constraint::observer TObserver, rpp::constraint::decayed_type Accumulator>
    struct reduce_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
        using Seed                                       = rpp::utils::extract_observer_type_t<TObserver>;
 
        RPP_NO_UNIQUE_ADDRESS TObserver    observer;
        RPP_NO_UNIQUE_ADDRESS mutable Seed seed;
        RPP_NO_UNIQUE_ADDRESS Accumulator  accumulator;
 
        template<typename T>
        void on_next(T&& v) const
        {
            seed = accumulator(std::move(seed), std::forward<T>(v));
        }
 
        void on_error(const std::exception_ptr& err) const { observer.on_error(err); }
 
        void on_completed() const
        {
            observer.on_next(std::move(seed));
            observer.on_completed();
        }
 
        void set_upstream(const disposable_wrapper& d) { observer.set_upstream(d); }
 
        bool is_disposed() const { return observer.is_disposed(); }
    };
 
    template<rpp::constraint::decayed_type Seed, rpp::constraint::decayed_type Accumulator>
    struct reduce_t : lift_operator<reduce_t<Seed, Accumulator>, Seed, Accumulator>
    {
        using operators::details::lift_operator<reduce_t<Seed, Accumulator>, Seed, Accumulator>::lift_operator;
 
        template<rpp::constraint::decayed_type T>
        struct operator_traits
        {
            static_assert(std::is_invocable_r_v<Seed, Accumulator, Seed&&, T>, "Accumulator is not invocable with Seed&& abnd T returning Seed");
 
            using result_type = Seed;
 
            template<rpp::constraint::observer_of_type<result_type> TObserver>
            using observer_strategy = reduce_observer_strategy<TObserver, Accumulator>;
        };
 
        template<rpp::details::observables::constraint::disposables_strategy Prev>
        using updated_optimal_disposables_strategy = Prev;
    };
 
    template<rpp::constraint::observer TObserver, rpp::constraint::decayed_type Accumulator>
    struct reduce_no_seed_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
        using Seed                                       = rpp::utils::extract_observer_type_t<TObserver>;
 
        RPP_NO_UNIQUE_ADDRESS TObserver   observer;
        RPP_NO_UNIQUE_ADDRESS Accumulator accumulator;
        mutable std::optional<Seed>       seed{};
 
        template<typename T>
        void on_next(T&& v) const
        {
            if (seed.has_value())
                seed = accumulator(std::move(seed).value(), std::forward<T>(v));
            else
                seed = std::forward<T>(v);
        }
 
        void on_error(const std::exception_ptr& err) const { observer.on_error(err); }
 
        void on_completed() const
        {
            if (seed.has_value())
                observer.on_next(std::move(seed).value());
            observer.on_completed();
        }
 
        void set_upstream(const disposable_wrapper& d) { observer.set_upstream(d); }
 
        bool is_disposed() const { return observer.is_disposed(); }
    };
 
    template<rpp::constraint::decayed_type Accumulator>
    struct reduce_no_seed_t : lift_operator<reduce_no_seed_t<Accumulator>, Accumulator>
    {
        using lift_operator<reduce_no_seed_t<Accumulator>, Accumulator>::lift_operator;
 
        template<rpp::constraint::decayed_type T>
        struct operator_traits
        {
            static_assert(std::is_invocable_r_v<T, Accumulator, T&&, T>, "Accumulator is not invocable with T&& abnd T returning T");
 
            using result_type = T;
 
            template<rpp::constraint::observer_of_type<result_type> TObserver>
            using observer_strategy = reduce_no_seed_observer_strategy<TObserver, Accumulator>;
        };
 
        template<rpp::details::observables::constraint::disposables_strategy Prev>
        using updated_optimal_disposables_strategy = Prev;
    };
} // namespace rpp::operators::details
 
namespace rpp::operators
{
     * @see https://reactivex.io/documentation/operators/reduce.html
     */
    template<typename Seed, typename Accumulator>
        requires (!utils::is_not_template_callable<Accumulator> || std::same_as<std::decay_t<Seed>, std::invoke_result_t<Accumulator, std::decay_t<Seed> &&, rpp::utils::convertible_to_any>>)
    auto reduce(Seed&& seed, Accumulator&& accumulator)
    {
        return details::reduce_t<std::decay_t<Seed>, std::decay_t<Accumulator>>{std::forward<Seed>(seed), std::forward<Accumulator>(accumulator)};
    }

     *
     * @par Example
     * @snippet reduce.cpp reduce_no_seed
     *
     * @ingroup aggregate_operators
     * @see https://reactivex.io/documentation/operators/reduce.html
     */
    template<typename Accumulator>
    auto reduce(Accumulator&& accumulator)
    {
        return details::reduce_no_seed_t<std::decay_t<Accumulator>>{std::forward<Accumulator>(accumulator)};
    }
} // namespace rpp::operators