nwkcmk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, The foreach block below overwrite all the elements in @test with A. Can anybody tell me if this is a feature or a bug? 
 @test = (1,2,3,4);
 
 foreach my $_tempvar (@test) {
      $_tempvar = "A";
     } 
     
   print @test;

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Many thanks in advance!!

Replies are listed 'Best First'.
Re: foreach array manipulation
by ikegami (Patriarch) on Jan 26, 2005 at 06:45 UTC

    Feature. for/foreach variables are refences (in the C meaning) instead of copies. If you want to copy, try this:

    @test = (1,2,3,4);
 
foreach (@test) {
   my $_tempvar = $_;

   $_tempvar = "A";
} 
     
print @test;

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[d/l]
Re: foreach array manipulation
by monkfan (Curate) on Jan 26, 2005 at 06:40 UTC
    Hi,

    This is not a bug. You are assigning value "A" for the variable "$_tempvar". So it replace the orginal $_tempvar value which were taken from @test element originally.

    What are you trying to do exactly with $_tempvar?
    Perhaps you can tell us your intention, so we can give suggestions.

    Regards,
    Edward
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Re: foreach array manipulation
by Hena (Friar) on Jan 26, 2005 at 06:42 UTC
    I would say this is as it should be. As it allows you to change the values of the array with foreach loop, which is faster than others (for or while).
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      As it allows you to change the values of the array with foreach loop, which is faster than others (for or while).
      Huh?!? Maybe I misunderstood the sense of your words, but C<for> and C<foreach> are just synonims. Or were you referring to C-style C<for>'s (C<while>'s in disguise)?!?
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        According to the people "who wrote the book on Perl" {grin}, there is indeed a "for" loop (what you would call "C style"), and a "foreach" loop (stolen mostly from C-shell). Even though the keywords of "for" and "foreach" are interchangeable, we call a foreach loop a foreach loop even when it's spelled "f-o-r".

        -- Randal L. Schwartz, Perl hacker
        Be sure to read my standard disclaimer if this is a reply.

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        Yup, i do call '($i=0;$i<$j;$i++) {}' a for loop and 'foreach (@list) {}' a foreach loop. I don't use 'for (@list) {}' inorder to avoid confusion like this :).

        But thanks for merlyn for info on what others think.
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Re: foreach array manipulation
by nwkcmk (Sexton) on Jan 26, 2005 at 07:01 UTC
    Thanks everybody!! It is clear to me now.
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Re: foreach array manipulation
by blazar (Canon) on Jan 26, 2005 at 08:48 UTC
    Feature. Clearly documented too...
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