when<TResult extends Object?>  method 
      
  
TResult
when<TResult extends Object?>()
      
      
    
A switch-like method, using callbacks.
As opposed to map, this offers destructuring.
It is equivalent to doing:
switch (sealedClass) {
  case Subclass(:final field):
    return ...;
  case Subclass2(:final field2):
    return ...;
}
Implementation
@optionalTypeArgs TResult when<TResult extends Object?>(TResult Function( int ttl,  bool prompt,  int tag)  $default,) {final _that = this;
switch (_that) {
case _RpcOptions():
return $default(_that.ttl,_that.prompt,_that.tag);}
}