dpp::when_any< Args > Class Template Reference

Experimental class to co_await on a bunch of awaitable objects, resuming when the first one completes. On completion, returns a result object that contains the index of the awaitable that finished first. A user can call result::index() and result::get<N>() on the result object to get the result, similar to std::variant. More...

Classes
struct	awaiter
	Object returned by operator co_await(). Meant to be used by the standard library, not by a user. More...
class	result
	Object returned by operator co_await() on resumption. Can be moved but not copied. More...

Public Member Functions
	when_any ()=default
	Default constructor. A when_any object created this way holds no state. More...
template<typename... Args_>
	when_any (Args_ &&... args)
	Constructor from awaitable objects. Each awaitable is executed immediately and the when_any object can then be co_await-ed later. More...
	when_any (const when_any &)=delete
	This object is not copyable. More...
	when_any (when_any &&) noexcept=default
	Move constructor. More...
	~when_any ()
	On destruction the when_any will try to call dpp::task::cancel() cancel() on each of its awaitable if they have such a method. More...
when_any &	operator= (const when_any &)=delete
	This object is not copyable. More...
when_any &	operator= (when_any &&) noexcept=default
	Move assignment operator. More...
bool	await_ready () const noexcept
	Check whether a call to co_await would suspend. More...
awaiter	operator co_await () noexcept
	Suspend the caller until any of the awaitables completes. More...

Detailed Description

template<typename... Args>
class dpp::when_any< Args >

Experimental class to co_await on a bunch of awaitable objects, resuming when the first one completes. On completion, returns a result object that contains the index of the awaitable that finished first. A user can call result::index() and result::get<N>() on the result object to get the result, similar to std::variant.

See also

when_any::result

Template Parameters

Args...

Type of each awaitable to await on

Constructor & Destructor Documentation

when_any() [1/4]

template<typename... Args>

dpp::when_any< Args >::when_any ( )

default

Default constructor. A when_any object created this way holds no state.

when_any() [2/4]

template<typename... Args>

template<typename... Args_>

dpp::when_any< Args >::when_any ( Args_ &&...  args )

inline

Constructor from awaitable objects. Each awaitable is executed immediately and the when_any object can then be co_await-ed later.

Exceptions

???	Any exception thrown by the start of each awaitable will propagate to the caller.

Parameters

args	Arguments to construct each awaitable from. The when_any object will construct an awaitable for each, it is recommended to pass rvalues or std::move.

when_any() [3/4]

template<typename... Args>

dpp::when_any< Args >::when_any ( const when_any< Args > &  )

delete

This object is not copyable.

when_any() [4/4]

template<typename... Args>

dpp::when_any< Args >::when_any ( when_any< Args > &&  )

defaultnoexcept

Move constructor.

~when_any()

template<typename... Args>

dpp::when_any< Args >::~when_any ( )

inline

On destruction the when_any will try to call dpp::task::cancel() cancel() on each of its awaitable if they have such a method.

Note

If you are looking to use a custom type with when_any and want it to cancel on its destruction, make sure it has a cancel() method, which will trigger an await_resume() throwing a dpp::task_cancelled_exception. This object will swallow the exception and return cleanly. Any other exception will be thrown back to the resumer.

Member Function Documentation

await_ready()

template<typename... Args>

bool dpp::when_any< Args >::await_ready ( ) const

inlinenoexcept

Check whether a call to co_await would suspend.

Note

This can change from false to true at any point, but not the other way around.

Returns

bool Whether co_await would suspend

operator co_await()

template<typename... Args>

awaiter dpp::when_any< Args >::operator co_await ( )

inlinenoexcept

Suspend the caller until any of the awaitables completes.

See also

result

Exceptions

???	On resumption, throws any exception caused by the construction of the result.

Returns

result On resumption, this object returns an object that allows to retrieve the index and result of the awaitable.

operator=() [1/2]

template<typename... Args>

when_any& dpp::when_any< Args >::operator= ( const when_any< Args > &  )

delete

This object is not copyable.

operator=() [2/2]

template<typename... Args>

when_any& dpp::when_any< Args >::operator= ( when_any< Args > &&  )

defaultnoexcept

Move assignment operator.