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0568d3bf0b
The `async_result` template now supports a new form:
template <typename CompletionToken, typename Signature>
struct async_result
{
typedef /* ... */ return_type;
template <typename Initiation,
typename RawCompletionToken,
typename... Args>
static return_type initiate(
Initiation&& initiation,
RawCompletionToken&& token,
Args&&... args);
};
The `initiate()` function must:
* Transform the token into a completion handler object `handler`.
* Cause the invocation of the function object `initiation` as if
by calling:
std::forward<Initiation>(initiation)(
std::move(handler),
std::forward<Args>(args)...);
The invocation of `initiation` may be deferred (e.g. lazily evaluated),
in which case `initiation` and `args` must be decay-copied and moved
as required.
A helper function template `async_initiate` has also been added as a
wrapper for the invocation of `async_result<>::initiate`. For backward
compatibility, this function supports both the old and new async_result
forms.