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Unless I totally misunderstood the above comments -- which is possible as I just briefly skimmed them -- the problem here is not that map and grep don't localize $_, but that they may execute code that may alter the value of $_, which in this case is aliased to a constant. Consider this code:

$_ = 'Ovid'; %hash = map { $_ => 1 } qw/ foo bar baz /; print;

That code will print 'Ovid' because $_ has been localized within the map statement. Now, if you try to alter the $_, your code fails because you're trying to alter a constant:

$_ = 'Ovid'; %hash = map { $_ .= 'asdf'; $_ => 1 } qw/ foo bar baz /; print;

To get around that, you can do this:

$_ = 'Ovid'; %hash = map { local $_ = $_; $_ .= 'asdf'; $_ => 1 } qw/ foo bar baz /; print;

That allows you to assign the aliased constant to a real variable, thus avoiding the problems outlined in this thread.


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In reply to Re: Re: while(<>) { ... } considered harmful by Ovid
in thread while(<>) { ... } considered harmful by IlyaM

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