bearophile wrote:
Michel Fortin:
But if one of your function has an 'out' parameter, it's impossible to
implement the strong guarantee, as illustrated by this trivial example:
void testOut(out int a) {
throw new Exception("hello!");
}
void main() {
int a = 2;
try
testOut(a);
finally
writeln(a);
}
Prints:
0
object.Exception: hello!
This happens because the out parameter gets reset to its default value
as soon as you enter the function, so you can't throw an exception
before it has been changed.
So should 'out' be reformed to behave more like a return value? I'm not
sure. But I think this is something to keep in mind when using out
parameters.
In a recent post here:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=110908
and in some successive answers I have tried to explain that out arguments are a
hack, they aren't as logically clean as multiple return values. I didn't think
about exceptions too, your example adds one more case to what I was saying
there. Thank you.
Bye,
bearophile
I re-read that recent post of yours in the context of this new post and
I must say that I agree with you. The ability to return mutiple return
values, as a tuple of sorts, is a good idea. Short of this a stronger
type system with existential typing (cardinalities) would suffice. Of
course that might bring us into a discussion about nullable types which
is which is which is which is which is a recursive topic on this ng.
Regards
Justin
