Care to explain why they are there if they are evil? I sort of like having a decent check that the arguments to my functions are sound (most languages provide this), and have only adopted using them in Perl lately -- despite some controversy. Coming from a C/C++ background, forward declarations are considered a good thing.

Is it true that in Perl a forward declaration is essentially a definition, and thus you run into problems with defining functions that never have a correctly defined body at a certain point in the code? That's the only reason I would think would make them a bad design choice.

I will accept the wisdom of folks in this thread saying "don't do it", but I'm a stubborn beast and I usually need to know why I am or am not doing something.

Care to explain why they are there if they are evil?

Tom Christiansen's good ol' Far More Than Everything You've Ever Wanted to Know about Prototypes in Perl explains prototypes quite nicely. It doesn't go as far as calling prototypes necessarily evil, but you can decide for yourself.

What about the performance increase you get from using prototypes? My understanding is that using prototypes gives you a circa 10% boost on performance. Is that not worth using them?

hackmare.

If you are still keen on using prototypes after having read the above comments, I thought I would throw out the answer you were originally looking for.

Throw in a 'use diagnostics;' at the top of your code, and you will get the following:

(W prototype) You've called a function that has a prototype before the parser saw a definition or declaration for it, and Perl could not check that the call conforms to the prototype. You need to either add an early prototype declaration for the subroutine in question, or move the subroutine definition ahead of the call to get proper prototype checking. Alternatively, if you are certain that you're calling the function correctly, you may put an ampersand before the name to avoid the warning. See perlsub.

This is telling you to put a forward declaration in your code that tells perl what the prototype of the function is, and stick it before the first use the function.

sub readConfig ($$);  # or whatever the prototype is
[download]

Check out perlsub for more details.

- Cees

You've specified a prototype with your function. Don't. Perl's prototypes are not like C or C++ or Java. Its actually an entirely different sort of thing.

You might also want to check out Devel::SummarizedWarnings if you're looking at too many identical errors.

Insert a declaration for the sub somewhere before you call it. You can leave the definition of the sub where it is. A declaration in perl is like sub myfoo ($$);.

When you use prototypes, perl wants you to declare the prototypes before you use them in the code.
If you put your subs before the main body of your script, then this will fix the problem

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There will be two of perl-related technical presentations.