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?

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

Module::Pluggable - perfect. Dispatch table - yep I can see how I might use that. Abstract factory pattern - this looks quite cool and I think I'll sit down one day and play with it.

Thanks.

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();
[download]

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

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