Does the Dart programming language have an equivalent to Javascript's "prototype"?

Question

In Dart, is it possible for a function to have a prototype associated with it?

Example Javascript code:

doStuff.prototype.isDefined = true; //is there anything like Javascript's function prototypes in Dart?
function doStuff(){
    console.log("The function doStuff was called!");
}

Is it possible to do the equivalent of this in Dart (i.e., create a list of properties for each function?)

Answer 1

Two things to address here:

First, Dart doesn't have prototypes or prototypal inheritance, and instead uses classical inheritance. Rather than a prototype, objects have a class, and instead of a prototype chain, objects have an super classes.

Second, for your specific case, I think we'd have to see more of what you need to do to figure out the idiomatic way to do it in Dart. It should soon be possible to emulate functions with objects so that you an invoke an object and still have state and other methods associated with it.

See this article for more: http://www.dartlang.org/articles/emulating-functions/

When that capability lands you'll be able to do this:

class DoStuff {
  bool isDefined = true;
  call() => print("The function doStuff was called!");
}
var doStuff = new DoStuff();

main() => doStuff();

Which works if you have a fixed set of metadata about your function that you need to keep track of. It's slightly different from the JavaScript because each instance of the function is Dart will have it's own state for isDefined. I'm not sure if it's possible or easy to get multiple instances of the function is JavasScript, but you might need to make isDefined static so that the value is shared across all instances.

Answer 2

Dart does not allow you to add or remove member variables from an instance of a class at runtime. Rewriting your example in Dart it might look something like this:

class doStuff {
  bool isDefined;
  doStuff() {
    isDefined = true;
  }
  void stuff() {
    print('The function stuff was called!');
  }
}

main() {
  new doStuff().stuff();
}

If you wanted to add a property bag to a class in Dart you would write:

class PropertyObject {
  Map<String, Dynamic> properties;

  PropertyObject() {
    properties = new Map<String, Dynamic>();
  }

  Dynamic operator[](String K) => properties[K];
  void operator[]=(String K, Dynamic V) => properties[K] = V;
}

main() {
  PropertyObject bag = new PropertyObject();
  bag['foo'] = 'world';
  print('Hello ${bag['foo']}');
}

Note that you can't access map properties using the '.' operator.