Using arbitrary packages

[Sprad]

I'd like to be able to do this:
use $foo;
where $foo contains some module name. But when I try, I get a syntax error. Is such a thing even possible?

[fergal]

eval "use $foo";
die $@ if $@ # die with error message if it failed

will do it but it will do it at runtime, whereas a genuine use will do it at compile time. If you do

BEGIN
{
  my $foo = get_a_module_name();
  eval "use $foo";
  die $@ if $@
}

it will happen at compile time, you just need to be careful that $foo has a value at compile time.

[ysth]

If $foo is trusted data, you can say eval "use $foo";, but that won't take effect at compile time. Starting with 5.6.2, you can say

   use if 1, $foo;

but $foo has to already be set at compile time, e.g.

   my $foo;
   BEGIN { $foo = $ENV{SERIALIZER} || "Storable" }
   use if 1, $foo;

but even that IMO is more clearly written as

   BEGIN { eval "use ".($ENV{SERIALIZER}||"Storable"); }

What exactly are you trying to accomplish? There's probably a better way.

[Sprad]

In a nutshell, I'd like to have a config file that contains module names and function names. I want to read the config file, 'use' all the modules, and then make the function calls as given in the config file.

It's all trusted data, since it's all being run locally.

[fergal]

Perhaps you should use

do $filename;

and have actual real Perl in the file that looks like

use Module1;
use Module2;
function1();
function2();

it will run faster. No point in inventing your own mini perl parser. Especially if in the future you decide you need to start adding arguments to your functions etc.

[PodMaster]

Starting with 5.6.2, you can say

Its more like starting with perl 5 (if its on CPAN, you can get it from CPAN) :D

[duff]

See Module::Load