run-time module usage

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

Fellow monks,

for some module, I need to include other modules based on run-time information. Here's roughly what I am doing right now:

    sub init {
        my ($someModule, $someCondition) = @_;

        eval "use Acme::$someModule";
        eval "use Funky::Library"
            if $someCondition;
    }

    init("Bleach", 1);
[download]

Now, for some reason, I don't really like eval "$some $code". I fear the performance hit (although I have no idea whether there really is one), and more importantly I just don't like the thought of compiling during runtime. I guess I could rewrite the code using require and import, like this:

    sub init {
        my ($someModule, $someCondition) = @_;

        require "Acme/$someModule.pm";
        import "Acme/$someModule.pm";

        if $someCondition {
            require Funky::Library;
            import Funky::Library qw(grooves moves);
        }
    }

    init("Bleach", 1);
[download]

Is this the canonical way to solve that problem; are there any issues I need to be aware of?

Comment on run-time module usage Select or Download Code

Replies are listed 'Best First'.
Re: run-time module usage by Courage (Parson) on Aug 02, 2002 at 19:54 UTC
Your guess is exactly right: namely, it really is a canonical way to solve your mentioned problem. You could add some error-checking using `eval { # your mentioned "require" and "import" statements go here } if ($@) { # something smells fishy here, or my name is Stinky Lulu }` [download] which is a special case of try-block. Courage, the Cowardly Dog.	[reply] [d/l]
Re: run-time module usage by Zaxo (Archbishop) on Aug 02, 2002 at 21:25 UTC
It's too new for this to be a general recommendation, but with perl-5.8.0 you can say: `use if $someCondition, 'Funky::Library';` [download] Yes, there is a pragmatic if.pm behind that. After Compline, Zaxo	[reply] [d/l]
Re: run-time module usage by crenz (Priest) on Aug 02, 2002 at 21:11 UTC
Update and Bonus Question: Consider `# 1 my $m = "Module.pm"; require $m; import $m qw(something); # 2 require "Module.pm"; import "Module.pm" qw(something);` [download] Number one works fine. Number two doesn't. Why? perl complains `String found where operator expected (...) (Do you need to predeclare import?)` [download] and under Windows, I even get a `Out of Memory`	[reply] [d/l] [select]