array ref 1

[rotis23]

Hi All,

Got a problem using a reference to a main array within a package.

Why does this not work:

my $smtp = Net::SMTP->new(\@main::SMTPServerList, Timeout => $main::SMTPServerTimeout);

and this work:

my @templist = @main::SMTPServerList;
my $smtp = Net::SMTP->new(\@templist, Timeout => $main::SMTPServerTimeout);

Cheers, rotis23

 

[ishnid]

What, exactly, do you mean by `not work' - what errors occur?

What about this?

my $smtp = Net::SMTP->new( [ @main::SMTPServerList ], Timeout => $main::SMTPServerTimeout);

 

[KevinADC]

In your example that works, you first create the array then create a reference to the array, that is why it works.

 

[fishiface]

How is @SMTPServerList declared or first used?

this works:

@list = (1,2,3);
package test;
sub deref {
        my $ref = $_[0];
        print join( ', ', @{$_[0]} );
}
deref \@main::list;

but make @list a lexical and it fails:

my @list = (1,2,3);
package test;
sub deref {
        my $ref = $_[0];
        print join( ', ', @{$_[0]} );
}
deref \@main::list;

although I couldn't tell you why. Anyone?

fish

"As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs."
--Maurice Wilkes

 

[rotis23]

sorry - "doesn't work" means that $smtp is undefined i.e. there was an error within the SMTP module.

ishnid - square brackets do work. Why?

fishiface - @SMTPServerList is declared in main as:

$SMTPServerList[0] = '127.0.0.1';
$SMTPServerList[1] = '127.0.0.2';

Thanks for your help people!

rotis23

 

[ishnid]

fish - lexicals are different to package variables, so when you declare a lexical called @list, it doesn't create a corresponding @main::list, which would be a different variable. To illustrate:

#!/usr/bin/perl -w
use strict;


@main::test = qw/ar afds/;
my @test = qw/blah blah/;

print @test, "\n";
print @main::test, "\n";

rotis23 - simple answer is that I don't know! It seems that the module was unable to see @main::SMTPServerList, though I can't think of a reason (unless you're changing the array after passing it in but before the module uses it, though that's pure speculation). The square brackets set up an anonymous array reference containing the same contents as @SMTPServerList and uses that instead of the original array itself. It's similar to the original solution you posted (with the temporary array), except that it requires less typing. Glad it worked.

 

[fishiface]

ishnid - thanks for answer. Can you point me to where I could read more on this and, specifically, when I should use lexicals instead of package variables?

thanks

"As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs."
--Maurice Wilkes

 

[ishnid]

There's an article here that I seem to remember being useful. Let me know what you think.

My general rule of thumb on scoping is that you should always use lexicals unless you have a specific reason not to.

 

[fishiface]

What an excellent FAQ. I'd strongly recommend it to anyone feeling a little fuzzy about $main::, my(), local() or our(). Thanks ishnid - have a star.

f

"As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs."
--Maurice Wilkes

 

[rotis23]

Yeah, thanks Ishnid.

I've just spent most of the afternoon on

http://perl.plover.com

and I've got very little coding done!!!