[Athens-pm] Perl oddities

[Mark Pors]

Giorgos Epitidios wrote:

>Good morning everybody. Yesterday I spoke about not being able to have one
>foreach loop inside another. That was wrong.  What you cannot do is play
>with the $_ variable inside a loop (if you want to keep your array elements
>intact). See the following example:
>
>sub func {
>   $_ = 100;
>}
>
>
>my @array = (1,2,3);
>
>print "before calling func\n";
>foreach ( @array ) {
>   print "$_\n";
>}
>print "calling func inside loop\n";
>foreach ( @array ) {
>   print "$_\n";
>   func;
>}
>print "after calling func\n";
>foreach ( @array ) {
>   print "$_\n";
>}
>
>What you get by running it is:
>
>before calling func
>1
>2
>3
>calling func inside loop
>1
>2
>3
>after calling func
>100
>100
>100
>
>As someone mentioned in the comp.lang.perl forum:
>
> Little known features of foreach.  The iteration variable used
> in the foreach is not a copy, but in fact an alias to the value,
> in this case $_.  Thus, when you change it you change the value
> in the array.
>
>So actually $_ IS each element of the array. This means that &func changes
>the array elements.
>
>Hope that is of interest to someone.
>
>
>Giorgos Epitidios
>
>P.S. My mistakes make me wiser
>  
>
:-)

this is why I do:

foreach $arr_value ( @array )

It's not as perly as foreach ( @array ), but a bit more clear (and safe)

Mark

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