in reply to While on hashes doesn't work?

Not recommending it, but perhaps it gives insight into how while works (in addition to what gellyfish said above)

#!/usr/bin/perl -w
use strict;

my %data = (    a01     => "two",
                a02     => "peas",
                a03     => "in",
                a04     => "a",
                a05     => "pod."
);

while (($_) = sort keys %data){

 print "while: $data{$_}\n";
 delete $data{$_};
}

print "while loop terminates because",
      "%data is now empty >", %data,"< \n";

__END__

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Without those parens around $_, I would expect it to try to pass '5' into the block (which it would do if you took away the sort function), but it doesn't do that. I suppose that might qualify as an insignificant bug.
update: thanks to merlyn for fixing the bug in my understanding of how sort behaves.
mkmcconn </code>

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Re: Re: While on hashes doesn't work?
by merlyn (Sage) on Feb 04, 2002 at 23:38 UTC 
    while (($_) = sort keys %data){ 
 
 print "while: $data{$_}\n"; 
 delete $data{$_}; 
}

    [download]
    This is a pretty expensive loop. You'd be much better doing: 
    while (my ($k, $v) = each %data) {
  print "key is $k, value is $v\n";
}

    [download]
    Without those parens around $_, I would expect it to try to pass '5' into the block (which it would do) if you took away the sort function, but it doesn't do that. I suppose that might qualify as an insignificant bug.
    No, sort in a scalar context always returns undef. Maybe someday, it'll return something useful. But not yet. No bug, except in perhaps your understanding. {grin}

    -- Randal L. Schwartz, Perl hacker

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