vinoth.ree has asked for the wisdom of the Perl Monks concerning the following question: 

 use Data::Dumper;
{
    my @arra = (10,20);
&doublevalue(*arra); 
}
sub doublevalue {
    local *a = shift ;
    print Dumper @a;
}

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In the above code I am passing type glob of *arra to the function doublevalue, in this function I am making *a as temporary alias to *arra, but in @a I am not getting the @arra values. What is the problem in this code ?

Replies are listed 'Best First'.
Re: type glob problem
by nagalenoj (Friar) on Mar 03, 2009 at 07:23 UTC
    You cannot use a lexically scoped array as a parameter, because lexical variables don't have typeglobs associated with them. Lexical variables won't be in symbol tables.
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Re: type glob problem
by ELISHEVA (Prior) on Mar 03, 2009 at 07:45 UTC
    Was this meant as an example to illustrate questions about how to work with globs or are you simply trying to pass a value into a function doublevalue(...)? The sample you have posted looks like a very old Perl coding style - what version of Perl are you working with?

    If the point was to pass values, the current way to pass values is to use variables and references, like this:

    use strict;
use warnings;
use Data::Dumper;
{
    my @arra = (10,20);

    #no need for & and you can just pass a reference
    #&doublevalue(*arra);
    doublevalue(\@arra); 
}

sub doublevalue {
  #my is preferred to local
  #local *a = shift ;
  my $a = shift;
  print Dumper @$a;
}

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    If you want to learn more about how type globs work, see perlref.

    Best, beth

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Re: type glob problem
by bichonfrise74 (Vicar) on Mar 03, 2009 at 07:37 UTC
    If you change this... 
    &doublevalue(\@arra);

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    This seems to work just fine for me, unless I'm missing something.
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Re: type glob problem
by Anonymous Monk on Mar 03, 2009 at 07:24 UTC
    you need to use references, see print shift; for clues
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Re: type glob problem
by boom (Scribe) on Mar 03, 2009 at 09:20 UTC

    You can pass in an ordinary reference to a subroutine expecting a type glob, and it will work fine.

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Re: type glob problem
by rir (Vicar) on Mar 03, 2009 at 22:11 UTC
    nagalenoj gave you the correct info; I'm just stating it another way. Your my @arra and your *arra are different and unrelated variables. The *arra is a package variable *main::arra which can, as a typeglob, refer to the variable @main::arra but that has nothing to do with a lexical, aka my, variable named @arra.

    You are passing an empty typeglob to doublevalue. This demonstrates that you are passing nothing, loosely speaking, to your function: 

     my @arra = (10,20);
 print ">@main::arra<$/";
 print ">>@arra<<$/";

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    Update: With your code, use warnings; would have flagged that the name main::arra was used only once, hinting at the problem. With use diagnostics; the message is more confusing as if it were written before lexical variables were added to the language.

    Be well,
    rir

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