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Re^5: It's a dog, but what kind? (polymorphism , in Perl OO) (!abstract)by tye (Cardinal)
|on Mar 23, 2004 at 23:06 UTC||Need Help??|
Yes, as I said, I understand the objection. I note that you don't quote what your alternative is nor acknowledge the problem that I was bringing up.
Did you give a concrete class when you asked your question? As I've said, I agree that there is a problem in theory, and that sometimes there is a problem in practice. But I've also found that, in practice, exactly what it means to get a 'new' object from an object of a *specific* class is often quite clear (and I don't think it usually means what you appear to be referring to as "clone" nor "copy").
You appear to be using "clone" to mean something close to "copy all of the object's attributes" and using "copy" (based on emphasis) to mean something close to "copy none of the object's attributes".
I don't think I've ever seen people talking about classes as having two types of attributes (that I'll define shortly). So I'm not surprised that asking questions in the abstract fail to get people to think about splitting attributes into two types. In practice, for many Perl classes, I think this split happens quite naturally.
I'll call the two types 'basis' attributes and 'convenience' attributes. The basis attributes are items that must be passed in to new(). The convenience attributes have more to do with the personal preferences of the user of the module.
$obj->new( $basis1, $basis2, ... ) creates a new object based on the passed-in basis attributes but copying the convenience attributes from $obj.
Now, some classes have attributes that don't clearly fall into one of these categories, and I suspect in that such cases the meaning of 'instance new' would not be as clear.
And I suspect that people who think $obj->new( ... ) should be "clone" are either thinking of convenience attributes or aren't thinking of the "..." part while people who think $obj->new( ... ) should do ref($obj)->new( ... ) aren't thinking of convenience attributes (that perhaps are more common in Perl OO than in other flavors of OO).