'This' type (original) (raw)
Neal Gafter neal at gafter.com
Tue Mar 3 13:26:25 PST 2009
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On Tue, Mar 3, 2009 at 1:18 PM, Marek KozieĊ <develop4lasu at gmail.com> wrote:
Oh.
I get it now. Yes A is a subtype of Collection but after B extends A B will be Collection from B point of view B will be Collection from A point of view In base relation is same as one created by overloaded methods.
So if we have a class C that is a sibling of B (a child of A), then from A's point of view we can place a C into the collection (because C is a subtype of A). But then from B's point of view the collection should contain only Bs and not any Cs. So when B pulls something out of the collection we could get a ClassCastException.
That's the kind of thing you need to demonstrate can't happen in order to show this change is a sound extension of the type system.
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