Dart example: Factory pattern, constructors, mixins

By Alvin Alexander. Last updated: March 16, 2022

I’m generally getting out of the writing business, but that being said, I don’t mind sharing some code as I go along. In this case I created the follow Dart programming examples as I reload Dart into my brain:

Dart Factory pattern/method example
Dart constructors with public and private fields
Dart mixin example

Dart Factory example

First, here’s a simple Dart Factory pattern/method example:

abstract class Dog {
    void speak();
    factory Dog.createDog(DogType dogType) {
        if (dogType == DogType.Small) {
            return Poodle();
        } else {
            return Rottweiler();
        }
    }
}

class Poodle implements Dog {
    void speak() => print('Imma Poodle');
}

class Rottweiler implements Dog {
    void speak() => print('Imma Rottweiler');
}

enum DogType {
    Small,
    Large
}

void main() {
    Dog d = Dog.createDog(DogType.Large);
    d.speak();
}

That example can be improved, but for today it’s an okay start.

Dart constructor examples and private fields

Next, here’s an example of Dart constructors and public and private fields:

// dart fields are public by default
class Person {
    String firstName;
    String lastName;
    Person(this.firstName, this.lastName);
}

// fields are private, so you need to define getters
// and setters when you want them
class PrivatePerson {
    String _firstName;
    String _lastName;
    PrivatePerson(this._firstName, this._lastName);
    // getters
    String get firstName => _firstName;
    String get lastName => _lastName;
    // setters
    void set firstName(String s) => _firstName = s;
    void set lastName(String s) => _lastName = s;
}

void main() {
    final p = Person('Alexander', 'Chigliak');
    p.firstName = 'Alex';
    p.lastName = 'Chiggy';
    print(p.firstName);
    print(p.lastName);

    final pp = PrivatePerson('Alexander', 'Chigliak');
    pp.firstName = 'Alvin';
    pp.lastName = 'Alexander';
    print(pp.firstName);
    print(pp.lastName);
}

A Dart mixin example

Finally, here’s a Dart mixin example. It’s a partial conversion of a Scala example I share in the Scala Cookbook:

// can make this 'class' or 'mixin'
mixin HasTail {
    void wagTail() => print("Tail is wagging");
    void stopTail() => print("Tail is stopped");
}

abstract class Pet {
    void speak() => print("Yo");
    void comeToMaster();
}

class Dog extends Pet with HasTail {
    void comeToMaster() => print("Woo-hoo, I'm coming!");
}

class Cat extends Pet with HasTail {
    void comeToMaster() => print("That’s not gonna happen.");
    void speak() => print("meow");
}

void main() {

    Dog dog = Dog();
    dog.speak();
    dog.comeToMaster();
   
    final cat = Cat();
    cat.speak();
    cat.comeToMaster();

}

In summary, if you needed some Dart programming examples, I hope those are helpful.

flutter

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