How do you say, in Perl....

[willymacoy]

I have come here for a few terms and concepts that I can chase down. If anyone can help, thanks in advance.

I wish to write a generic module that will take a undefined (in the unknown sense, rather than the undef sense) hash reference as a parameter. It will return a single value. The module will call, on a per machine basis, any other modules, or functions, that the user has decided need calling. The generic module needs to find these called modules by itself (kind of like Linux startup scripts) and load them (and preferably keep them loaded because they will be called aplenty).

What Perl concepts do I have to chase down to be able to do this?

Thanks

[SilasTheMonk]

The question seems pretty vague to me. I have the impression you are trying to do some sort of magic but aren't too clear what. Could you actually try and state what problem you are trying to solve?

[willymacoy]

I have a message I wish to send. I wish to sign it depending on the content of the message. There will be a default signature. But, if the user wishes he may intercept the signature routine and provide a different signature, by providing another module that is called by the signature routine - if it exists.

The programming of the signature routines is quite basic. It is just the strategy of having them called without the calling code explicitly call them. After all, I don't know what they are going to be, just that they might be.

Does that make sense?

[Anonymous Monk]

In addition to Re: How do you say, in Perl...., see Module::Pluggable, and dispatch table , Abstract factory pattern/ http://perldesignpatterns.com/?AbstractFactory

See also Re^2: LWP to open a new browser window for a practical example of the concept

[oxone]

You might want to pass in a code ref instead of a hash ref, and then in your function you can say:

my $signature = $custom_coderef ? $custom_coderef->() : default_sig();

The code ref itself can require any modules it needs, eg:

my $coderef = sub{
  require Foo::Bar;
  my $signature = "blah";
  return $signature;
}

[Anonymous Monk]

What Perl concepts do I have to chase down to be able to do this?

perlintro, Simple Module Tutorial, use, require, Module::Load, Module::List...

[sundialsvc4]

The general notion of “wrapping things,” ... the so-called “onion approach” ... might be the sort of thing that you are looking for.   As an example of the idea, look at Plack::Builder, which is part of a so-called “web server super-glue” system that needs a lot of flexibility.   (Nevermind the system.   Observe the concept and its implementation.   By the way, “DSL” means “domain-specific language,” which was a new terminology to me.)

Before pursuing strategies like, “I wish to write a generic module that will take a hash reference as a parameter ...” it is usually wisdom to initially restrain such thoughts and let your CPAN do the walking before you let your fingers do the typing.   Presume that you will probably be able to find something that is suitable without having to build it.   Not always the case, but usually a fruitful way ... in my experience, a much more fruitful way ... to arrange your initial thoughts regarding a problem like this one.   Or I think so, anyway...

(And if you do come up with something original and stunning ... “Wow!   Your first CPAN contribution!   Gee, thanks!!”   Lookin’ forward to it ... seriously.)