execution::split: Conflict between shared_state<Child_Sndr> and shared_state<Out_Sndr>

[mochunshuang]

split_t

struct split_t
{
    template <snd::sender Sndr>
        requires(snd::sender_in<Sndr, split_env>)
    auto operator()(Sndr &&sndr) const // noexcept
    {
        auto dom = snd::general::get_domain_early(std::as_const(sndr));
        return snd::transform_sender(
            dom, snd::make_sender(*this, {}, std::forward<Sndr>(sndr)));
    }

    template <snd::sender Sndr>
    auto transform_sender(Sndr &&sndr) noexcept // NOLINT
        requires(snd::sender_for<decltype((sndr)), split_t>)
    {
        // TODO(mcs):
        // Note: tag_change: split_t => split_impl_tag
        // Note: data_change: {} => shared_wrapper(shared_state{child},old_tag)
        // Note: sh_state: shared_state<child_sndr> conflict shared_state<Sndr>
        auto &&[old_tag, _, child] = sndr;
        auto *sh_state =
            new __split::shared_state{std::forward_like<decltype(sndr)>(child)};
        return snd::make_sender(split_impl_tag(),
                                __split::shared_wrapper{sh_state, old_tag});
    }
};
inline constexpr split_t split{}; // NOLINT

local_state

 template <class Sndr, class Rcvr>
    struct local_state : local_state_base
    {                          // exposition only
        using onstopcallback = // Note: Rcvr + get_stop_token_t => token_type
            stop_callback_of_t<queries::stop_token_of_t<queries::env_of_t<Rcvr>>,
                               snd::general::on_stop_request>;

        ~local_state() noexcept override;
        void notify() noexcept override;

        local_state(Sndr &&sndr, Rcvr &rcvr) noexcept;

        local_state(local_state &&) = delete;
        local_state(const local_state &) = delete;
        local_state &operator=(local_state &&) = delete;
        local_state &operator=(const local_state &) = delete;

        std::optional<onstopcallback> on_stop; // exposition only // NOLINT

        // using Childen = snd::__detail::mate_type::child_type<Sndr>;
        shared_state<Sndr> *sh_state; // exposition only // NOLINT
        Rcvr *rcvr;                   // exposition only // NOLINT
    };

template <> // for tag: adapt::split_impl_tag
struct snd::general::impls_for<adapt::split_impl_tag> : snd::__detail::default_impls
{
    // Note: create [basic_state->state] when connect. 
    static constexpr auto get_state = // NOLINT
        []<class Sndr>(Sndr &&sndr, auto &rcvr) noexcept {
            // Note: call: local_state(sndr,rcvr)
            return adapt::__split::local_state{std::forward_like<Sndr>(sndr), rcvr};
        };
   ....
}

p2300R10
local-state(Sndr&& sndr, Rcvr& rcvr) noexcept;
Effects: Equivalent to:

// when tag is split_impl_tag 
auto& [_, data, _] = sndr; //snd::make_sender(split_impl_tag(),__split::shared_wrapper{sh_state, old_tag}); //only can bind 2 but 3
this->sh_state = data.sh_state.get(); //shared_state<child_sndr> conflict shared_state<Sndr>
this->sh_state->inc-ref();
this->rcvr = addressof(rcvr);

info

 sender auto input = just(1);
 sender auto multi_shot = split(std::move(input));
 sender auto start =
        then(multi_shot, [](int i) { std::cout << i << " First continuation\n"; });
sync_wait(std::move(start));

`
e:\0_github_project\mcsexec\mcsexec\test\test_base\split.cpp:79:32: required from here
79 | mcs::this_thread::sync_wait(std::move(start));
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
E:/0_github_project/mcsexec/mcsexec/include/__detail/adapt/__split.hpp:254:35: error: cannot convert 'mcs::execution::adapt::__split::shared_state<mcs::execution::snd::__detail::basic_sender<mcs::execution::factories::__just_tmcs::execution::recv::set_value_t, mcs::execution::snd::__detail::product_type > >' to 'mcs::execution::adapt::__split::shared_state<mcs::execution::snd::__detail::basic_sender<mcs::execution::adapt::split_impl_tag, mcs::execution::adapt::__split::shared_wrapper<mcs::execution::adapt::__split::shared_state<mcs::execution::snd::__detail::basic_sender<mcs::execution::factories::__just_tmcs::execution::recv::set_value_t, mcs::execution::snd::__detail::product_type > >, mcs::execution::adapt::split_t> > >' in assignment
254 | this->sh_state = data.sh_state; // TODO(mcs): ? ~~~~~^~~~~~~~
| |
| mcs::execution::adapt::__split::shared_state<mcs::execution::snd::__detail::basic_sender<mcs::execution::factories::__just_tmcs::execution::recv::set_value_t, mcs::execution::snd::__detail::product_type > >*

`

[jiixyj]

Agreed, this seems to be a bug in the spec. local-state's sh_state type should not be shared-state<Sndr>* as specified, but something like shared_state_of_data<Sndr>* where shared_state_of_data is the decayed type of the (exposition only) sh_state member of the data member of the Sndr, i.e. the instance of shared-wrapper.

Also, I don't see where the get() in this->sh_state = data.sh_state.get(); (https://eel.is/c++draft/exec#split-6) comes from.

In any case, the split as defined in the working draft has some issues related to cancellation behavior, so I guess it is not unlikely to receive a respec or even getting removed from the draft altogether.