template< typename CancellationHandler> decay< CancellationHandler >::type & assign( CancellationHandler && handler);
Destroys any existing handler in the slot, then installs the new handler, constructing it as a decay-copy of the supplied handler.
The handler is a function object to be called when the signal is emitted. The signature of the handler must be
The handler to be installed.
A reference to the newly installed handler.