signatures - Subroutine signatures with no source filter


version 0.14


    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.


Bugs may be submitted through the RT bug tracker (or


Florian Ragwitz <>


  • Karen Etheridge <>

  • Peter Martini <>

  • Father Chrysostomos <>

  • Alex Kapranoff <>

  • Steffen Schwigon <>

  • Alexandr Ciornii <>

  • Dave Mitchell <>


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.