Re: Is Dynamic Object Decoration Possible

The problem with the implicit wrapper sollution is that the new type is "MyTrait[T]" not, T with MyTrait. Meaning that the wrapper doesn't have the same methods as T.
One sollution that might work right now is to use a DynamicProxy[1] to wrap the object in and cast it to T with MyTrait.
If I'm not mistaken Scala generates Interface instances for most things, and as long as you can pass those instances to the proxy factory you should be fine.
BR, John

[1] http://java.sun.com/j2se/1.3/docs/guide/reflection/proxy.html
On Fri, Jan 16, 2009 at 7:14 PM, Kris Nuttycombe <kris [dot] nuttycombe [at] gmail [dot] com> wrote:

This is generally what implicit conversions are used for.

trait MyTrait[T] {
  def myObject : T
  def myMethod = {
    //...
  }
}

implicit def decorate[T](o : T) : MyTrait[T] = new MyTrait[T] {
  override def myObject = o
}

Then, whenever you have an instance of whatever the decorated type is, you can do

val o = new Foo()

o.myMethod

Kris

On Fri, Jan 16, 2009 at 10:30 AM, Bastian, Mark <mbastia [at] sandia [dot] gov> wrote:

Scala gives you the powerful ability to create object factories that decorate the primary object wth a trait like so with no explicit class definition:   def objectWithTrait = new MyObject with MyTrait   Is it possible to dynamically decorate an object, like so:   def decorate(o : Object) : Object = o with MyTrait   I suppose you could make a cloning factory that does something like this:   def cloneAndDecorate(o : MyObject) {   //foo and bar are copy constructor fields   new o(o.foo, o.bar) with MyTrait }   This might be adequate in some situations, but it might be nice to be able to dynamically add the trait. Can it be done?   Thanks, Mark