dart: Will objects created in a recurring function be cached or recreated?

Question

In recurring functions such as CustomPaint()'s paint(), if I create an object this way:


void paint(Canvas canvas, Size size) {
    
  ....
  
  var myObj = MyClass();
  var myObj.configure(canvas, size);
 
  ....
    
}

Will this object get recreated while paint() gets called every frame or will it be cached until something it depends on such as screen size changes?

Alex Radzishevsky · Accepted Answer · 2020-07-27 08:05:08Z

3

It depends on how you implement MyClass constructor. I can see several options:

MyClass standard constructor - then object will be recreated every time it is called;
MyClass can have const constructor. Then if you create instance with const MyClass() it will be same instance. Therefore it is not always possible to do that.
MyClass can have default factory constructor. This way you can implement "caching" inside MyClass itself depending on your requirements. Example is "singleton" - you will always have single instance. See here for example: How do you build a Singleton in Dart?

Please note also that if objects of MyClass are lightweight it could be that you do not need to optimize: Dart is usually good creating lots of small objects and garbage collecting them.

answered Jul 27, 2020 at 8:05

Alex Radzishevsky

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