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How do I import a global variable form a package with require?

by nysus (Parson)
on Jul 22, 2021 at 13:47 UTC ( #11135292=perlquestion: print w/replies, xml ) Need Help??

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

Monks, I was toying around with importing/requiring to improve my aptitude with them. So I have this package:
#! /usr/bin/env perl package A; require Exporter; our @ISA = qw(Exporter); our @EXPORT_OK = qw (sub1 $var); our %EXPORT_TAGS = (all => [ qw(sub1 $var) ]); our $var = 7; sub sub1 { print "this\n"; } 1;

I want to use require to import the $var global. I try this:

#! /usr/bin/env perl use strict; use warnings; use lib '.'; require A; A->import (':all'); sub1(); print $var . "\n";

This script throws Global symbol "$var" requires explicit package name (did you forget to declare "my $var"?).

But I have no such error with Use A like so:

#! /usr/bin/env perl use strict; use warnings; use lib '.'; use A ':all'; print $var . "\n";

So I have a gap in my knowledge. I'm not sure why the second way works and the first doesn't. Any guidance is appreciated. Thanks!

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate Priest Vicar";
$nysus = $PM . ' ' . $MCF;
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Re: How do I import a global variable form a package with require?
by choroba (Archbishop) on Jul 22, 2021 at 13:53 UTC
    A->import happens at runtime, but use happens at compile time. The strict check happens at compile time, too, so use a BEGIN block to run the import before the variable is encountered:
    BEGIN { require A; A->import(':all'); } print $var;
    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
      Alternatively, declare the variable for the compiler. The call to import then assigns the value. This prints 7 (with your A.pm):
      #! /usr/bin/env perl use strict; use warnings; our $var; use lib '.'; require A; A->import (':all'); print $var . "\n";

      Ah, yes, I remember that. However, what if I want to only import $var at runtime? Am I just stuck fully qualifiying it with A::var? And I still don't get why sub1 imports just fine with require and $var doesn't.

      $PM = "Perl Monk's";
      $MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate Priest Vicar";
      $nysus = $PM . ' ' . $MCF;
      Click here if you love Perl Monks

        > what if I want to only import $var at runtime?

        What does it mean? If you have code that will be compiled at runtime, it works:

        require A; A->import('$var'); eval 'print $var; 1' or warn $@;

        > why sub1 imports just fine with require and $var doesn't

        Strict checks that variables are declared before you use them. It doesn't check subs when it's sure it's a sub, i.e. when parentheses follow the sub name. Try using sub1 without parentheses: the compiler will only see a bareword, not a sub call, and will complain.

        Update: reworded.

        map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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