The composer functor

ReduCpp@composer.hpp

template <class A, class ...Reducers>
class reducpp::composer {
public:
    using ReducersTuple = std::tuple<std::decay_t<Reducers> ...>;
    using CompositeState = std::tuple<typename reducpp::_impl::reducer_traits<Reducers>::state_t ...>;

    composer(const Reducers& ...reducers)
        : m_reducers(reducers...) { }

    CompositeState operator() (const CompositeState& state, const A& action) {
        return apply(state, action, std::index_sequence_for<Reducers...>{});
    }

    template <std::size_t ...Is>
    CompositeState apply(const CompositeState& state, const A& action, std::index_sequence<Is...>) {
        return { std::get<Is>(m_reducers)(std::get<Is>(state), action) ... };
    }

private:
    const ReducersTuple m_reducers;
};