I am explicitly attempting to retain the exit value of loop counter. This behaviour is implicitly overriding that attempt -- in order to provide a behaviour that is available to me explicitly, by declaring the loop variable within the for loop construct for my $n ( ... )

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I would prefer that implicit behaviours would take a back seat to explicit behaviours. In most cases, perl gets that right (IMO), but in this instance, probably as a matter of history, I think it gets this wrong.

You're confusing implicit and explicit behaviours. foreach is an explicit aliasing construct and never behaves any differently.

This is a conscious design decision. It's not going to change come Perl 6 either. Aliasing is not reasonably feasible if you want to retain the value past the loop, unless you're willing to introduce convoluted semantics about when the value retained is a copy and when it is still an alias. Your proposed semantics would therefor have to be implemented as something along the lines of "aliasing when my, copying when absent". Of course that would require some extra special case treatment of $_.

I'd prefer simply having foreach be consistent with itself even if there wasn't a lot of legacy code to cater for. So I'll say that Perl got this one right.