when<TResult extends Object?>  method 
- @optionalTypeArgs
- TResult $default(- Ed25519HDPublicKey accountKey,
- List<int> writableIndexes,
- List<int> readonlyIndexes
 
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( Ed25519HDPublicKey accountKey,  List<int> writableIndexes,  List<int> readonlyIndexes)  $default,) {final _that = this;
switch (_that) {
case _MessageAddressTableLookup():
return $default(_that.accountKey,_that.writableIndexes,_that.readonlyIndexes);case _:
  throw StateError('Unexpected subclass');
}
}