NAME

Acme::Signature::Arity - provides reliable, production-ready signature introspection

DESCRIPTION

You'll know if you need this.

If you're just curious, perhaps start with https://www.nntp.perl.org/group/perl.perl5.porters/2021/11/msg262009.html.

No part of this is expected to work in any way when given a sub that has a prototype. There are other tools for those: Sub::Util.

For subs that don't have a prototype, this is also not expected to work. It might help demonstrate where to look if you wanted to write something proper, though.

Exported functions

arity

Returns the UNOP_aux details for the first opcode for a coderef CV. If that code uses signatures, this might give you some internal details which mean something about the expected parameters.

Expected return information, as a list:

• number of required scalar parameters

• number of optional scalar parameters (probably because there are defaults)

• a character representing the slurping behaviour, might be '@' or '%', or nothing (undef?) if it's just a fixed list of scalar parameters

This can also throw exceptions. That should only happen if you give it something that isn't a coderef, or if internals change enough that the entirely-unjustified assumptions made by this module are somehow no longer valid. Maybe they never were in the first place.

max_arity

Takes a coderef, returns a number or undef.

If the code uses signatures, this tells you how many parameters you could pass when calling before it complains - undef means unlimited.

Should also work when there are no signatures, just gives undef again.

min_arity

Takes a coderef, returns a number or undef.

If the code uses signatures, this tells you how many parameters you need to pass when calling - 0 means that no parameters are required.

Should also work when there are no signatures, returning 0 in that case.

coderef_ignoring_extra

Given a coderef, returns a coderef (either the original or wrapped) which won't complain if you try to pass more parameters than it was expecting.

This is intended for library authors in situations like this:

 $useful_library->each(sub ($item) { say "item here: $item" });

where you later want to add optional new parameters, and don't trust your users to include the mandatory , @ signature definition that indicates excess parameters can be dropped.

Usage - let's say your first library version looked like this:

 sub each ($self, $callback) {
  my $code = $callback;
  for my $item ($self->{items}->@*) {
   $code->($item);
  }
 }

and you later want to pass the index as an extra parameter, without breaking existing code that assumed there would only ever be one callback parameter...

 sub each ($self, $callback) {
  my $code = coderef_ignoring_extra($callback);
  for my $idx (0..$#{$self->{items}}) {
   $code->($self->{items}{$idx}, $idx);
  }
 }

Your library is now at least somewhat backwards-compatible, without sacrificing too many signature-related arity checking features: code expecting the new version will still complain if required parameters are not provided.

AUTHOR

TEAM@cpan.org

WARRANTY

None, it's an Acme module, you shouldn't even be reading this.

INHERITED METHODS

Exporter

as_heavy, export, export_fail, export_ok_tags, export_tags, export_to_level, import, require_version

cpanm Acme::Signature::Arity

perl -MCPAN -e shell
install Acme::Signature::Arity