Re: [chuck-users] Casting behaviour

17 Oct 2014

      On 18/10/2014 1:40 am, Michael Heuer wrote:
...
Gonzalo wrote:
...
I have this (unexpected?) behaviour when casting. I can cast a object to its
parent class, but the methods that get executed are still their own (and
viceversa). I.e.:
----------------------------------
public class Parent {
   fun void test() {
     <<< "Parent" >>>;
   }
}
class Child extends Parent {
   fun void test() {
     <<< "Child" >>>;
   }
}
Parent p;
Child @ ch;
p $ Child @=> ch;
ch.test(); // prints Parent
This shouldn't work, because p !instanceof Child, the cast should be a
compiler error.
Thanks Michael. You're right, and in fact it doesn't work at all. Now 
that I've tried, ch can not call methods exclusive to Child either 
(Assertion failed: (m_offset < obj->vtable->funcs.size()), function 
execute, file chuck_instr.cpp, line 4765).
...
...
Is this intended behavior? What's the point of casting then?
I typically only use casting when pulling object references out of
data structures that hold arrays of Object references, e.g. an
ArrayList
https://github.com/heuermh/lick/blob/master/Freeze.ck#L73
Of course, I see. I was trying to use casting to bypass the lack of 
constructors, bad misuse.
...
...
I might describe too what I'm trying to do, maybe there's a better approach.
I have a .create method in Parent that returns a Parent object, and I wanted
to create that same method in Child, but I can't do it because the arguments
are the same, and it won't let me overwrite the method when only the return
type changes. So to create a child with the .create method, I do this:
Parent.create(...) $ Child @=> Child ch;
Which works, but then it still behaves as a parent, so it defeats the whole
purpose.
Having proper constructors in ChucK would help here
https://github.com/spencersalazar/chuck/issues/32
A workaround might be to include the classname in your create methods
class Parent {
   fun static Parent createParent(...) { }
}
class Child extends Parent {
   fun static Child createChild(...) { }
}
Yes, that might be the way to go. I use init() methods as a workaround 
for constructors, so my normal instantiations look like:

MyClass c;
c.init(...);

Not very nice, which is why I was trying to have the static 'create' 
methods. I'm thinking of having a global Make class, and put all my 
static initializers there. Which would look something like:

class Make {
   fun static Parent Parent(args) {
     Parent p;
     p.init(args);
     return p;
   }
   ....
}

Make.Parent(...) @=> Parent p;

Ugly class, but nicer to call than Parent.createParent(args) ?
...
michael
_______________________________________________
chuck-users mailing list
chuck-users@lists.cs.princeton.edu
https://lists.cs.princeton.edu/mailman/listinfo/chuck-users