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An initiating function produces its return type as follows:
— constructing an object result of type async_result<decay_t<CompletionToken>,
Signature>, initialized as result(completion_handler);
and
— using result.get() as the operand of the return statement.
[Example: Given an asynchronous operation with Completion
signature void(R1 r1, R2 r2), an initiating function
meeting these requirements may be implemented as follows:
template<class CompletionToken>
auto async_xyz(T1 t1, T2 t2, CompletionToken&& token)
{
typename async_result<decay_t<CompletionToken>, void(R1, R2)>::completion_handler_type
completion_handler(forward<CompletionToken>(token));
async_result<decay_t<CompletionToken>, void(R1, R2)> result(completion_handler);
// initiate the operation and cause completion_handler to be invoked with
// the result
return result.get();
}
For convenience, initiating functions may be implemented using the async_completion
template:
template<class CompletionToken>
auto async_xyz(T1 t1, T2 t2, CompletionToken&& token)
{
async_completion<CompletionToken, void(R1, R2)> init(token);
// initiate the operation and cause init.completion_handler to be invoked
// with the result
return init.result.get();
}
—end example]