[Kc] subroutine parameter list

Andrew Hanenkamp sterling at hanenkamp.com
Wed Apr 9 12:29:56 PDT 2008

On Wed, Apr 9, 2008 at 12:14 PM, James Carman <developer at peelle.org> wrote:

> Hey all,
> Is it possible to do something like:
> &param_test("somestring", "another_string" $arrayref);
> sub param_test($tom; $george; @$array) {
>     print $tom;
>     ....;
> }
> #################
> I am wanting to Specifiy how many arguments to take. Also I want to
> specify the name of the arguments. And also if possible the type of the
> arguments.

Perl's concept of a subroutine prototype is unusual and there are some
purists who will tell you to never use them. I think they are helpful when
used carefully. In this case, this is about the best you can do:

sub param_test($$\@) {
    my ($tom, $george, $array_param) = @_;

You would then call the subroutine (make sure you *don't* use &param_test()
or Perl will ignore the prototype):

param_test("somestring", "otherstring", @array);

The other alternative would be to declare param_test() like this:

sub param_test($$@) {
    my ($tom, $george, @array_param) = @_;

This could be called exactly the same way as before. The significant
difference between the two is that in the first one, the $array_param
variable is actually a references to the \@array passed, which means you can
modify it in place. In the second case, you don't have a direct reference to
the @array value to modify.

The good thing is that if you call param_test() this way, it will warn you
during compile that something isn't right when you try to use it without
three parameters, specifically two scalars followed by an array.

That's about it for compile time checking. For more details, you can see the
"Prototypes" section of perlsub (
http://search.cpan.org/search?query=perlsub&mode=all). If you want robust
runtime checking, I second Andy's recommendation of Param::Validate.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.pm.org/pipermail/kc/attachments/20080409/699bcb05/attachment.html 

More information about the kc mailing list