Factory constructor in Dart

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/

Hi Sharad,

Factory 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