java aliasing rules
Tom Tromey
tromey@redhat.com
Wed Mar 27 13:53:00 GMT 2002
>>>>> "Dan" == Dan Nicolaescu <dann@godzilla.ICS.UCI.EDU> writes:
Dan> Given this code:
Dan> class first { int i; char a; char f1; char f2; double d;};
Dan> class second { char b; char f2; int f3;};
Dan> public class t
Dan> {
Dan> public void f (first ps1, second ps2)
Dan> {
Dan> ps1.f1++;
Dan> ps2.f2++;
Dan> ps1.f1++;
Dan> ps2.f2++;
Dan> }
Dan> }
Dan> can it be assumed that given that "first" and "second" are
Dan> incompatible
Yes.
Dan> The more general question is if 2 COMPONENT_REFs that refer to
Dan> classes that are in conflicting alias sets (ie
Dan> alias_sets_conflict_p) alias in java. I have a hunch that this
Dan> might be true, but I don't know enough about java to be sure. If
Dan> the above is not true, is there a restricted case when it is
Dan> true?
My understanding, and please if you don't mind clear things up if I'm
wrong, is that each front end is free to write its own aliasing
function. And as far as I know gcj doesn't have one. So I don't know
how conflicting alias sets for Java are currently computed, but I
imagine it is just very conservative and doesn't follow the language
rules.
Better aliasing support is definitely something we'd like. It's on my
to-do list (and, I'd wager, Bryce's), but I haven't had time to look
at it.
Anyway, in Java, casts are *always* done according to the type system.
There is no way to circumvent it. So in your above example, it is
never possible to turn a `first' into a `second' -- they are not
compatible.
Does this answer your questions?
Tom
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