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a coderef, or if internals change enough that the entirely-unjustified assumptions made by this module are somehow no longer valid.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.