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How Do You Build a Singleton in Dart?

Chloe Bennett • • 13 min read
How Do You Build a Singleton in Dart?

The singleton pattern ensures only one instance of a class is ever created. How do I build this in Dart?

2

31 Answers

1
2

Thanks to Dart's factory constructors, it's easy to build a singleton:

class Singleton {
  static final Singleton _singleton = Singleton._internal();

  factory Singleton() {
    return _singleton;
  }

  Singleton._internal();
}

You can construct it like this

main() {
  var s1 = Singleton();
  var s2 = Singleton();
  print(identical(s1, s2));  // true
  print(s1 == s2);           // true
}
19

Here is a comparison of several different ways to create a singleton in Dart.

1. Factory constructor

class SingletonOne {

  SingletonOne._privateConstructor();

  static final SingletonOne _instance = SingletonOne._privateConstructor();

  factory SingletonOne() {
    return _instance;
  }

}
Chloe Bennett
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Chloe Bennett

Chloe Bennett explores the intersection of pop culture, streaming entertainment, digital trends, and contemporary lifestyle. Her weekly commentary reaches thousands of culture enthusiasts.