shared_task.md

Phantom.Coroutines

shared_task.h

shared_task.h provides an extensible shared_task<Result> implementation for implementing lazily-started coroutines that have can have multiple awaiters and can be copied and moved.

The result type of the task is a value reference to the type parameter to task<Result> unless the task returns void.

The default return type of the task is void, so a typical usage is:

shared_task<> DoSomethingThatDoesntReturnAnything() { co_return; }

shared_task<typename Result = void>

shared_task<Result> is an alias for basic_shared_task<shared_task_promise<Result>>.

shared_task_promise<typename Result, is_shared_task_promise_policy Policies...>

This alias template provides a basic_shared_task_promise with the requested policies applied.

basic_shared_task<typename Promise>

shared_task<Result> is an alias for basic_shared_task<shared_task_promise<Result>>.

basic_shared_task_promise<typename Result, ...>

basic_shared_task_promise implements the behavior of a shared task promise. It accepts explicitly selected policies. Typically, users extending shared_task should extend shared_task_promise<...>, as its type parameters are documented.

Extending shared tasks

Policy selection

It is possible to use non-default policies to the shared_task classes without performing explicit extension. The typical way to do so is to declare an alias template:

class other_promise{};

template<typename Result = void>
using waited_on_by_other_promise_task_type 
= 
basic_shared_task<
    shared_task_promise<
        continuation_type<std::coroutine_handle<other_promise>>
    >
>;

Now, waited_on_by_other_promise_task_type can be used like a shared_task<>:

task<> OtherFunction();

waited_on_by_other_promise_task_type<int> MyFunction()
{
    co_await OtherFunction();
    co_return 6;
}

Extension

shared_task<> is backed by the extension mechanisms in []extensible_promise.h](extensible_promise.md).