lambda

lambda is a helper function which wraps a function-like object to extend it's lifetime for the duration of the async operation. Primarily intended to be used with lambdas with captures as arguments to race_and_cancel and such.

The returned wrapper is callable with the same arguments as the original function object, and the arguments get forwarded to it.

Prototype

template <typename Fn>
lambda_callable lambda(Fn fn);

Requirements

Fn is a function-like object that produces a sender.

Arguments

• fn - the function-like object to wrap.

Return value

This function returns a wrapper object that upon being called returns a sender of unspecified type. The sender forwards the return value from the sender returned by fn.

Examples

async::run(
	async::race_and_cancel(
		async::lambda(
			[x_ = std::make_shared<int>(1)] (async::cancellation_token ct)
			-> async::result<void> {
				// x_ is valid here
				std::cout << *x_ << "\n";
				co_return;
				/* ... */
			}
		),
		[x_ = std::make_shared<int>(2)] (async::cancellation_token ct)
		-> async::result<void> {
			// x_ is NOT valid here
			// the hidden lambda `this` is out of scope!
			// std::cout << *x_ << "\n"; // crash !
			co_return;
		}
	)
);

Output:

1