NAME

Filter::signatures - very simplicistic signatures for Perl < 5.20

SYNOPSIS

    use Filter::signatures;
    no warnings 'experimental::signatures'; # does not raise an error
    use feature 'signatures'; # this now works on <5.20 as well

    sub hello( $name ) {
        print "Hello $name\n";
    }

    hello("World");

    sub hello2( $name="world" ) {
        print "Hello $name\n";
    }
    hello2(); # Hello world

DESCRIPTION

This module implements a backwards compatibility shim for formal Perl subroutine signatures that were introduced to the Perl core with Perl 5.20.

CAVEATS

The technique used is a very simplicistic transform to allow for using very simplicistic named formal arguments in subroutine declarations. This module does not implement warning if more or fewer parameters than expected are passed in.

The module also implements default values for unnamed parameters by splitting the formal parameters on /,/ and assigning the values if @_ contains fewer elements than expected. Function calls as default values may work by accident. Commas within default values happen to work due to the design of Filter::Simple, which removes them for the application of this filter.

Note that this module inherits all the bugs of Filter::Simple and potentially adds some of its own. Most notable is that Filter::Simple sometimes will misinterpret the division operator / as a leading character to starting a regex match:

    my $wait_time = $needed / $supply;

This will manifest itself through syntax errors appearing where everything seems in order. The hotfix is to add a comment to the code that "closes" the misinterpreted regular expression:

    my $wait_time = $needed / $supply; # / for Filter::Simple

A better hotfix is to upgrade to Perl 5.20 or higher and use the native signatures support there. No other code change is needed, as this module will disable its functionality when it is run on a Perl supporting signatures.

Line Numbers

Due to a peculiarity of how Filter::Simple treats here documents in some versions, line numbers may get out of sync if you use here documents.

If you spread your formal signatures across multiple lines, the line numbers may also go out of sync with the original document.

Comments within signatures

The module does not support comments within signatures

  sub invalid (
      $name,     # use this as the name
      $location, # use this as the location
  ) {
      "This is an example"
  }

The workaround is to not do that or to upgrade to Perl 5.20 or higher and use the native signatures support there.

eval

Filter::Simple does not trigger when using code such as

  eval <<'PERL';
      use Filter::signatures;
      use feature 'signatures';

      sub foo (...) {
      }
  PERL

So, creating subroutines with signatures from strings won't work with this module. The workaround is to upgrade to Perl 5.20 or higher.

Deparsing

The generated code does not deparse identically to the code generated on a Perl with native support for signatures.

ENVIRONMENT

If you want to force the use of this module even under versions of Perl that have native support for signatures, set $ENV{FORCE_FILTER_SIGNATURES} to a true value before the module is imported.

SEE ALSO

"Signatures" in perlsub

signatures - a module that doesn't use a source filter but optree modification instead

Sub::Signatures

REPOSITORY

The public repository of this module is http://github.com/Corion/filter-signatures.

SUPPORT

The public support forum of this module is https://perlmonks.org/.

BUG TRACKER

Please report bugs in this module via the RT CPAN bug queue at https://rt.cpan.org/Public/Dist/Display.html?Name=Filter-signatures or via mail to filter-signatures-Bugs@rt.cpan.org.

AUTHOR

Max Maischein corion@cpan.org

COPYRIGHT (c)

Copyright 2015-2016 by Max Maischein corion@cpan.org.

LICENSE

This module is released under the same terms as Perl itself.

cpanm Filter::signatures

perl -MCPAN -e shell
install Filter::signatures