Beefy Boxes and Bandwidth Generously Provided by pair Networks
Think about Loose Coupling

Re: Re: while(<>) { ... } considered harmful

by Ovid (Cardinal)
on Sep 08, 2002 at 00:58 UTC ( #195948=note: print w/replies, xml ) Need Help??

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

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.


Join the Perlmonks Setiathome Group or just click on the the link and check out our stats.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://195948]
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others imbibing at the Monastery: (11)
As of 2016-10-26 10:26 GMT
Find Nodes?
    Voting Booth?
    How many different varieties (color, size, etc) of socks do you have in your sock drawer?

    Results (340 votes). Check out past polls.