when<TResult extends Object?>  method 
- @optionalTypeArgs
- required TResult mentionRule(- MentionRule data
 
- required TResult followerRule(- FollowerRule data
 
- required TResult followingRule(- FollowingRule data
 
- required TResult listRule(- ListRule data
 
- required TResult unknown(),
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?>({required TResult Function( MentionRule data)  mentionRule,required TResult Function( FollowerRule data)  followerRule,required TResult Function( FollowingRule data)  followingRule,required TResult Function( ListRule data)  listRule,required TResult Function( Map<String, dynamic> data)  unknown,}) {final _that = this;
switch (_that) {
case UFeedThreadgateAllowMentionRule():
return mentionRule(_that.data);case UFeedThreadgateAllowFollowerRule():
return followerRule(_that.data);case UFeedThreadgateAllowFollowingRule():
return followingRule(_that.data);case UFeedThreadgateAllowListRule():
return listRule(_that.data);case UFeedThreadgateAllowUnknown():
return unknown(_that.data);}
}