template< typename CancellationHandler, typename... Args> CancellationHandler & emplace( Args &&... args);
Destroys any existing handler in the slot, then installs the new handler,
constructing it with the supplied
The handler is a function object to be called when the signal is emitted. The signature of the handler must be
Arguments to be passed to the
A reference to the newly installed handler.
Handlers installed into the slot via
are not required to be copy constructible or move constructible.