vistor_promise
A visitor_promise<T> is an extension of simple_promise that allows deferred execution of some function/s to “visit” or “preview” the returned type. visitor_promise<T> satisfies the Returnable concept.
The visitor_promise<T> allows the user to save a/many callable/s of signature void(T&) which will executed during the final suspend phase of the coroutine (after co_return is called). If multiple callable’s are saved, they will be executed in reverse order of deferment.
A code block can be deferred by using the co_yield (VistorBlock<T>) operator. All deferred code blocks can be removed through the co_yeild (purge_block) operator. These operators do not actually suspend the coroutine.
Example
/*
* template<typename T = void>
* using visitor_future = simple_future<T, visitor_promise<T>>;
*
* This function would return 3.
*/
visitor_future<std::size_t>
always_odd() noexcept
{
co_yield defer_block(
[this, code_]
(std::size_t& _size) noexcept
{
std::cout << "Tried to return " << _size << "\n";
/* Make sure the return value is odd... */
_size |= 1;
}
);
co_return 2;
/* The defer blocks will run after this return... */
}
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template<typename T = void>
class zab::visitor_promise : public zab::simple_promise<void> Public Functions
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inline auto get_return_object() noexcept
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inline decltype(auto) data() noexcept
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inline auto final_suspend() noexcept
- template<typename Functor> inline requires (std::is_nothrow_invocable_v< Functor, typename simple_promise< T >::returns & >) auto yield_value(defer_block< Functor > &&_block)
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inline auto yield_value(purge_block&&)
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inline auto get_return_object() noexcept
