Pass class reference to function?

[John Chipps-Harding]

Hi:

Is it possible to pass a reference to a class? E.g.:

Object instanciateThisClass(Class clazz) {
  return new clazz();
}

I have searched but cannot seem to find a solution.

Any help greatly appreciated!

Regards:


John

[Srinivas JONNALAGADDA]

On Tuesday, 30 October 2012 18:03:16 UTC+5:30, John Chipps-Harding wrote:

Is it possible to pass a reference to a class? E.g.:

Object instanciateThisClass(Class clazz) {
  return new clazz();
}

I have searched but cannot seem to find a solution.

 

        You can try the following John.

import 'dart:mirrors' as Mirrors;

class A {

  int i = 0;

  A(this.i);

}

Future foo(ClassMirror classMirror) {

  var newInstance = null;

  var future = classMirror.newInstance('', [42]);

  future.then((val) {

    newInstance = val.reflectee;

    print(newInstance);

    print(newInstance.runtimeType);

    print(newInstance.i);

  });

  return future;

}

main() {

  var obj = new A(4);

  var instanceMirror = Mirrors.reflect(obj);

  var classMirror = instanceMirror.type;

  var future = foo(classMirror);

  Futures.wait([future]);

}

- |0|0|

____

http://oneofmanyworlds.blogspot.com

[Vyacheslav Egorov]

Lightweight solution would be to just use closures instead of mirrors:

instantiate(f) {
return f();
}

instantiate(() => new A());
instantiate(() => new B());


--
Vyacheslav Egorov

> --
> Consider asking HOWTO questions at Stack Overflow:
> http://stackoverflow.com/tags/dart
>
>

[Gilad Bracha]

The latter is your best option. Pretty soon, you will be able to pass classes as objects, but you still won't be able to call new on them.  Using mirrors is possible, but much too heavyweight.  Also, at the moment, they only work on the VM. When they do work in dart2js, you will need to exercise judgement because they may increase your download size substantially (depending what you do and what your alternatives are).

--
Cheers, Gilad

[Srinivas JONNALAGADDA]

On Tuesday, 30 October 2012 23:15:34 UTC+5:30, Gilad Bracha wrote:

The latter is your best option. Pretty soon, you will be able to pass classes as objects, but you still won't be able to call new on them.  Using mirrors is possible, but much too heavyweight.  Also, at the moment, they only work on the VM. When they do work in dart2js, you will need to exercise judgement because they may increase your download size substantially (depending what you do and what your alternatives are).

         Agreed, Gilad!  By the way, what operations shall be permitted on class objects?  Construction is ruled out based on what you have said.  Static method invocation?  What else?  Thanks.

[Lasse R.H. Nielsen]

The current Type objects have no methods except what they inherit from Object. Of those, only toString is special in that it gives the name of the type.

All you can use them for is to get that name, and to use as an input to the mirror system if you want to mirror a class.

/L

-- 

Lasse R.H. Nielsen - l...@google.com  

'Faith without judgement merely degrades the spirit divine'
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