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is rw trait's effect on signature

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From:
Aaron Sherman
Date:
May 6, 2004 10:39
Subject:
is rw trait's effect on signature
Message ID:
1083865176.4985.88.camel@pps
There's a subtle problem / feature resulting from the "is rw" trait that
may be so obvious that I'm making a fool of myself, or it might be that
it's not yet occurred, but I don't recall seeing discussion of it.

The simple case is:

	sub foo(X $i is rw) {...}
	class X {...}
	class Y {...}
	my Y $var = 'something';
	foo($var);

In this case, something kind of interesting has to happen.

Either the signature checking has to verify that Y isa X (and thus can
be used polymorphically as X, not just converted to X) ...

... or, it has to do something of the sort:

	{ my X $tmp = $var; foo($tmp); $var = $tmp; }

which has its own problems, of course.

Were either of these the intention or am I missing something?

"is ref" probably has the same concern.
-- 
Aaron Sherman <ajs@ajs.com>
Senior Systems Engineer and Toolsmith
"It's the sound of a satellite saying, 'get me down!'" -Shriekback



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