Factory constructor in Dart

Question

how to create a factory constructor in dart.

Vulpes · Answer

Code examples for Dart are rather thin on the ground just now but there's one which involves a factory constructor here: http://www.dartexperience.com/en/tag/ejemplos/

Satyapriya Nayak · Answer

Hi Sharad, F actory Constructor :- This constructor does not create a new instance of the class but returns an instance based on logic like Singleton or from a cache. The code below shows a Singleton implementation. The _internal is basically like a private constructor used from the factory constructor to internally create an instance. class Config { static Config cfg ; int x; factory Config(){ if(cfg==null) { cfg = new Config._internal(); } return cfg; } Config._internal(){} } The snippet shown below will print 10 proving that factory constructor is returning the same instance every time it is invoked. void main() { Config c = new Config(); c.x =10; c = new Config(); print(c.x); } There is another type of constructor called Constant Constructors used to create compile time constant or immutable object using const keyword as shown below: class Test{ final int x,y; const Test (this.x,this.y); } Constant object with identical properties are basically the same object instance. So the code below will print true. void main() { var a = const Test(10,20); var b = const Test(10,20); print(a==b); } Please refer the below link http://codingndesign.com/blog/?p=278 Thanks