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Re^6: why need my in a foreach loop? (Aliasing)

by LanX (Canon)
on Dec 08, 2010 at 13:00 UTC ( #876015=note: print w/ replies, xml ) Need Help??


in reply to Re^5: why need my in a foreach loop?
in thread why need my in a foreach loop?

Hi Gabor

>However I'd be interested to know in what case would you really want to write such code?

As already said my is much younger than foreach and it's consistent and backward compatible.

While looping over localized globals could also be done with an extra local $packvar=$lex_for_var, the aliasing effect of foreach can't be achieved in any other way in core Perl.

$\="\n"; our $foo; sub f { $foo++ } my ($a,$b,$c)=(0)x3; for $foo ($a,$b,$c) { f(); # increments $a,$b,$c } print ($a,$b,$c); #: 111 for my $foo ($a,$b,$c) { f(); # nada } print ($a,$b,$c); #: 111 for my $x ($a,$b,$c) { local $foo=$x; f(); # nada } print ($a,$b,$c); #: 111 { my $foo; sub g { $foo++ } for $foo ($a,$b,$c) { g(); # nada (irritatingly) } print ($a,$b,$c); #: 111 }

For a detailed discussion, see How do closures and variable scope (my,our,local) interact in perl?.

Cheers Rolf

UPDATE: expanded code, fixed typos


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