Before my last commit a clone could not contain its own properties
(only traps) and =='d the clonee. This was behaviour explicitly
specified in the original xwt reference, but its not clear what the
benefit was.
In any case a clone of an object now contains properties & does not ==
the clonee. Overcoming these two trivial limitations makes the cloning
system behave like prototype based object inheritance in standard
javascript, though with a couple of advantages:
- objects have a clean namespace. The type system and management of
the keys is done through the operators keysof & instanceof.
- traps
This example code should explain the process and potential quite well:
var sword = {
damage: 4 ,
image: "sword.png",
attack: "swing"
};
var charm = function(o){
var r = sys.clone(o);
r.damage = o.damage+2;
r.attack ++= function(){
return "sparkle,"+cascade;
};
return r;
};
var magicsword = charm(sword);
assert(magicsword!=sword);
assert(magicsword instanceof sword);
assert(6==magicsword.damage);
assert("sparkle,swing"==magicsword.attack);
assert("sword.png"==magicsword.image);
assert(4==sword.damage);
assert("swing"==sword.attack);
assert("sword.png"==sword.image);
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