Singleton Pattern

In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one "single" instance. This is useful when exactly one object is needed to coordinate actions across the system. The term comes from the mathematical concept of a singleton.

• The abstract factory, builder, and prototype patterns can use singletons in their implementation.
• Facade objects are often singletons because only one facade object is required.
• State objects are often singletons.

Singletons are often preferred to global variables because:

• They do not pollute the global namespace (or, in languages with nested namespaces, their containing namespace) with unnecessary variables.[4]
• They permit lazy allocation and initialization, whereas global variables in many languages will always consume resources.

Wikipedia: Singleton Pattern

Example

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class Me {
  static final Me _singleton = new Me._internal();
  static final String _name = "Tyler";

  factory Me() {
    return _singleton;
  }

  static String get name => _name;
 
  @override
  String toString() => "Hello, my name is $name.";

  Me._internal();
}

void main() {
  var tyler = Me();
  var anotherTyler = Me();
  
  print(tyler);
  print(anotherTyler);

  var samenessCheck = identical(tyler, anotherTyler)
      ? "We are both the same ${Me.name}."
      : "We are NOT the same. I mean, just look at us.";
  print(samenessCheck);

  /*
    Hello, my name is Tyler.
    Hello, my name is Tyler.
    We are both the same Tyler.
  */
}