Re: What I Most Recently Learned in Perl, But Should Have Already Known


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Re: What I Most Recently Learned in Perl, But Should Have Already Known

by wfsp (Abbot)

on Aug 17, 2006 at 11:03 UTC ( [id://567884]=note: print w/replies, xml )

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in reply to What I Most Recently Learned in Perl, But Should Have Already Known

Using a foreach loop on an AoH creates an alias of the hash which goes out of scope after the loop.

#!/usr/bin/perl 

use strict;
use warnings;

my $recs = [
  # short records for brevity
  {id => 1},
  {id => 2},
  {id => 3},
];

my $rec;

for $rec (@{$recs}){
  # $rec is an alias...
  if ($rec->{id} == 1){
    last;
  }
}

# ... which is now out of scope :-(
print "$rec->{id}\n"; # Use of uninitialized value...

# what I should have done
($rec) = grep {$_->{id} == 1} @{$recs};

print "$rec->{id}\n"; # 1
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Re^2: What I Most Recently Learned in Perl, But Should Have Already Known by pKai (Priest) on Aug 17, 2006 at 22:55 UTC
`# $rec is an alias...` It's the previously declared lexical, implicitly localized. See perldoc perlsyn... Shorter example, without the need to blame AoH for the problem: `my $var = 4; for $var (1 .. 9) { last if $var == 7; } print $var; # prints: 4` [download]	[reply] [d/l] [select]

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