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Re: question about: my $a AND sort {$a <=> $b} keys %hash

by Discipulus (Canon)
on Aug 06, 2015 at 09:13 UTC ( [id://1137632]=note: print w/replies, xml ) Need Help??


in reply to question about: my $a AND sort {$a <=> $b} keys %hash

you must receive an error even without warnings enabled:
Can't use "my $a" in sort comparison at pmonks06082015.pl line 4.

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In short, never use $a and $b in your programs. It is explicitly mentioned in perlvar
$a
$b
Special package variables when using sort(), see sort. Because of this
+ specialness $a and $b don't need to be declared (using use vars , or
+ our()) even when using the strict 'vars' pragma. Don't lexicalize th
+em with my $a or my $b if you want to be able to use them in the sort
+() comparison block or function.

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L*
There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.

Replies are listed 'Best First'.
Re^2: question about: my $a AND sort {$a <=> $b} keys %hash
by Laurent_R (Canon) on Aug 06, 2015 at 09:29 UTC 
    Don't lexicalize them with my $a or my $b if you want to be able to us
+e them in the sort() comparison block or function.

    [download]
    But, on the other hand you can localize them when needed: 
    $ perl -we '
   local $a = 1;
   @h = sort {$a <=> $b} keys %hash;
   print "@h\n";> %hash = map { $_ , undef } 0 .. 3;
   @h = sort {$a <=> $b} keys %hash;
   print "@h\n";
'
0 1 2 3

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