A basic interface

// A person. The implicit interface contains greet(). class Person { // In the interface, but visible only in this library. final String _name; // Not in the interface, since this is a constructor. Person(this._name); // In the interface. String greet(String who) => 'Hello, $who. I am $\_name.'; } // An implementation of the Person interface. class Impostor implements Person { String get _name => ''; String greet(String who) => 'Hi $who. Do you know who I am?'; } String greetBob(Person person) => person.greet('Bob'); void main() { print(greetBob(Person('Kathy'))); // Hello, Bob. I am Kathy. print(greetBob(Impostor())); // Hi Bob. Do you know who I am? }