Create extension method in Dart

Question

Normally When I create a custom class I can create a function that uses that class as a parameter for example:

class Sphere{
    double calculateRadius() {return 40.0;}
}

So I can then call Sphere.calculateRadius().

But with pre-existing classes like for example the String one, this can't be done. For Example. I've tried doing something like:

String.createFrom(String s){return "new";}

but it doesn't work (Android Studio doesn't even make me compile.).

Is this possible, and if it is, how could I do it in Dart? And If I created it, how would I access the object I called the method from? (the String in the example)

Answer 1

As of now January 2020, Dart 2.7 officially introduced extension methods. To extend a class, this can be done:

extension NewExtension on double {
  int get myMethod {
    return (1/this*10).toInt();
  }
}

Answer 2

You probably mean extension methods. That's not yet supported but the Dart team made attempts already to design such a feature and the chances are good it will be added to the language

https://github.com/dart-lang/language/issues/41