Functions and constants functions

Returns at once if the operation has finished, otherwise suspends the calling task until the operation completes; the scheduler thread runs other tasks meanwhile. Throws like co_await: GetResults throws winrt::hresult_error for a failed operation and winrt::hresult_canceled for a canceled one. Task or converted thread only. Sets the operation's Completed handler, which an operation accepts only once. The task may resume on another scheduler thread: use agile objects only (the WinRT default; not objects bound to a single-threaded apartment). Initialize the multithreaded apartment once for the process, e.g. winrt::init_apartment() on the main thread, so that the scheduler threads belong to it implicitly. There is no timed variant: a timed-out wait would leave the handler behind with a reference to the task's stack.

Satisfied by IAsyncAction, IAsyncOperation<TResult>, IAsyncActionWithProgress<TProgress> and IAsyncOperationWithProgress<TResult, TProgress>, and by every type with the same Status, Completed and GetResults members.