How to do it...

Let's start building our own custom types in Dart:

1. First, define a class called Name, which is an object that stores a person's first and last names:

class Name {
 final String first;
 final String last;

 Name(this.first, this.last);


 @override
 String toString() {
 return '$first $last';
 }
}

2. Now, let's define a subclass called OfficialName. This will be just like the Name class, but it will also have a title:

class OfficialName extends Name {
 // Private properties begin with an underscore
 final String _title;
 
 // You can add colons after constructor
 // to parse data or delegate to super
 OfficialName(this._title, String first, String last)
 : super(first, last);

 @override
 String toString() {
   return '$_title. ${super.toString()}';
 }
}

3. Now, we can see all these concepts in action by using the playground method:

void classPlayground() {
  final name = OfficialName('Mr', 'Francois', 'Rabelais');
  final message = name.toString();
  print(message);
}

4. Finally, add a call to classPlayground in the main method:

main() {
  ...
  classPlayground();
}