cast<R> method
Adapt this stream to be a Stream<R>.
If this stream already has the desired type, its returned directly.
Otherwise it is wrapped as a Stream<R> which checks at run-time that
each data event emitted by this stream is also an instance of R.
Implementation
Stream<R> cast<R>() {
Stream<Object> self = this;
return self is Stream<R> ? self : retype<R>();
}