Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery

Variable as module name?

by Cody Fendant (Friar)
on Feb 01, 2013 at 22:25 UTC ( #1016618=perlquestion: print w/replies, xml ) Need Help??
Cody Fendant has asked for the wisdom of the Perl Monks concerning the following question:

I want to do this:

use Foo; my $object = Foo->new();

Only I want to replace 'Foo' with a variable determined by some other factor.

my $module_name = 'Foo'; use $module_name; my $object = $module_name->new();

I got as far as understanding that use will never be happy with this, is that right? And I ought to use require instead?

My code doesn't give an error if I do this:

$module = 'Foo'; my $module_path = $module . '.pm'; require $module_path;

But it complains that I'm calling "new" on an unblessed reference when I do my $object = $module->new(); on the next line.

Replies are listed 'Best First'.
Re: Variable as module name?
by kennethk (Abbot) on Feb 01, 2013 at 23:03 UTC

    You cannot use use in this context because it is wrapped in an implicit BEGIN block (see BEGIN, UNITCHECK, CHECK, INIT and END), and thus gets evaluated at compile time and before you could initialize the value of your variable. The usual work around here is to use a string eval, a la:

    my $module_name = 'Foo'; eval "use $module_name;1;" or die "Couldn't use $module_name: $@";
    Of course, this has security implications, since you are evaluating arbitrary code, depending on where your value comes from.

    But it complains that I'm calling "new" on an unblessed reference when I do my $object = $module->new(); on the next line.

    This should not be happening. The following code works for me (assuming an OO-module Foo in your path):

    #!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $module = 'Foo'; my $module_path = "$"; $module_path =~ s|::|/|g; require $module_path; print Dumper $module->new;

    Note the s|::|/|g to allow non-root modules. Also note that by requiring you are bypassing the import mechanism.

    #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

      Thank you very much, that's all working fine now. My unblessed reference problem was an unrelated error in my module.
Re: Variable as module name? (modern perl)
by Anonymous Monk on Feb 01, 2013 at 23:27 UTC

    Module::Pluggable, if

    stupid pet tricks :)

    $ perl -we " use if eval{require CGI}, our $cgi = 'CGI'; print $cgi->n +ew->header " Content-Type: text/html; charset=ISO-8859-1

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://1016618]
Approved by ww
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others romping around the Monastery: (4)
As of 2018-06-24 00:40 GMT
Find Nodes?
    Voting Booth?
    Should cpanminus be part of the standard Perl release?

    Results (126 votes). Check out past polls.