signatures(3) Subroutine signatures with no source filter


version 0.13


use signatures;
sub foo ($bar, $baz) {
return $bar + $baz;


With this module, we can specify subroutine signatures and have variables automatically defined within the subroutine.

For example, you can write

    sub square ($num) {
        return $num * $num;

and it will be automatically turned into the following at compile time:

    sub square {
        my ($num) = @_;
        return $num * $num;

Note that, although the syntax is very similar, the signatures provided by this module are not to be confused with the prototypes described in perlsub. All this module does is extracting items of @_ and assigning them to the variables in the parameter list. No argument validation is done at runtime.

The signature definition needs to be on a single line only.

If you want to combine sub signatures with regular prototypes a "proto" attribute exists:

    sub foo ($bar, $baz) : proto($$) { ... }


If you want subroutine signatures doing something that this module doesn't provide, like argument validation, typechecking and similar, you can subclass it and override the following methods.

proto_unwrap ($prototype)

Turns the extracted $prototype into code.

The default implementation returns "my (${prototype}) = @_;" or an empty string, if no prototype is given.

inject ($offset, $code)

Inserts a $code string into the line perl currently parses at the given $offset. This is only called by the "callback" method.

callback ($offset, $prototype)

This gets called as soon as a sub definition with a prototype is encountered. Arguments are the $offset within the current line perl is parsing and extracted $prototype.

The default implementation calls "proto_unwrap" with the prototype and passes the returned value and the offset to "inject".


prototypes aren't checked for validity yet
You won't get a warning for invalid prototypes using the "proto" attribute, like you normally would with warnings enabled.
you shouldn't alter $SIG{__WARN__} at compile time
After this module is loaded you shouldn't make any changes to $SIG{__WARN__} during compile time. Changing it before the module is loaded or at runtime is fine.


Moritz Lenz and Steffen Schwigon for documentation review and improvement.


Florian Ragwitz <[email protected]>



This software is copyright (c) 2008 by Florian Ragwitz.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.