NAME¶
MooseX::Method::Signatures - Method declarations with type constraints and no
source filter
SYNOPSIS¶
package Foo;
use Moose;
use MooseX::Method::Signatures;
method morning (Str $name) {
$self->say("Good morning ${name}!");
}
method hello (Str :$who, Int :$age where { $_ > 0 }) {
$self->say("Hello ${who}, I am ${age} years old!");
}
method greet (Str $name, Bool :$excited = 0) {
if ($excited) {
$self->say("GREETINGS ${name}!");
}
else {
$self->say("Hi ${name}!");
}
}
$foo->morning('Resi'); # This works.
$foo->hello(who => 'world', age => 42); # This too.
$foo->greet('Resi', excited => 1); # And this as well.
$foo->hello(who => 'world', age => 'fortytwo'); # This doesn't.
$foo->hello(who => 'world', age => -23); # This neither.
$foo->morning; # Won't work.
$foo->greet; # Will fail.
DESCRIPTION¶
Provides a proper method keyword, like "sub" but specifically for
making methods and validating their arguments against Moose type constraints.
SIGNATURE SYNTAX¶
The signature syntax is heavily based on Perl 6. However not the full Perl 6
signature syntax is supported yet and some of it never will be.
Type Constraints¶
method foo ( $affe) # no type checking
method bar (Animal $affe) # $affe->isa('Animal')
method baz (Animal|Human $affe) # $affe->isa('Animal') || $affe->isa('Human')
Positional vs. Named¶
method foo ( $a, $b, $c) # positional
method bar (:$a, :$b, :$c) # named
method baz ( $a, $b, :$c) # combined
Required vs. Optional¶
method foo ($a , $b!, :$c!, :$d!) # required
method bar ($a?, $b?, :$c , :$d?) # optional
Defaults¶
method foo ($a = 42) # defaults to 42
Constraints¶
method foo ($foo where { $_ % 2 == 0 }) # only even
Invocant¶
method foo ( $moo) # invocant is called $self and is required
method bar ($self: $moo) # same, but explicit
method baz ($class: $moo) # invocant is called $class
Labels¶
method foo (: $affe ) # called as $obj->foo(affe => $value)
method bar (:apan($affe)) # called as $obj->foo(apan => $value)
Traits¶
method foo (Affe $bar does trait)
method foo (Affe $bar is trait)
The only currently supported trait is "coerce", which will attempt to
coerce the value provided if it doesn't satisfy the requirements of the type
constraint.
Placeholders¶
method foo ($bar, $, $baz)
Sometimes you don't care about some params you're being called with. Just put
the bare sigil instead of a full variable name into the signature to avoid an
extra lexical variable to be created.
Complex Example¶
method foo ( SomeClass $thing where { $_->can('stuff') }:
Str $bar = "apan",
Int :$baz! = 42 where { $_ % 2 == 0 } where { $_ > 10 } )
# the invocant is called $thing, must be an instance of SomeClass and
has to implement a 'stuff' method
# $bar is positional, required, must be a string and defaults to "apan"
# $baz is named, required, must be an integer, defaults to 42 and needs
# to be even and greater than 10
BUGS, CAVEATS AND NOTES¶
This module is as stable now, but this is not to say that it is entirely bug
free. If you notice any odd behaviour (messages not being as good as they
could for example) then please raise a bug.
Fancy signatures¶
Parse::Method::Signatures is used to parse the signatures. However, some
signatures that can be parsed by it aren't supported by this module (yet).
No source filter¶
While this module does rely on the hairy black magic of Devel::Declare it does
not depend on a source filter. As such, it doesn't try to parse and rewrite
your source code and there should be no weird side effects.
Devel::Declare only effects compilation. After that, it's a normal subroutine.
As such, for all that hairy magic, this module is surprisingly stable.
What about regular subroutines?¶
Devel::Declare cannot yet change the way "sub" behaves. However, the
signatures module can. Right now it only provides very basic signatures, but
it's extendable enough that plugging MooseX::Method::Signatures signatures
into that should be quite possible.
What about the return value?¶
Type constraints for return values can be declared using
method foo (Int $x, Str $y) returns (Bool) { ... }
however, this feature only works with scalar return values and is still
considered to be experimental.
Interaction with Moose::Role¶
Methods not seen by a role's "requires"
Because the processing of the MooseX::Method::Signatures "method" and
the Moose "with" keywords are both done at runtime, it can happen
that a role will require a method before it is declared (which will cause
Moose to complain very loudly and abort the program).
For example, the following will not work:
# in file Canine.pm
package Canine;
use Moose;
use MooseX::Method::Signatures;
with 'Watchdog';
method bark { print "Woof!\n"; }
1;
# in file Watchdog.pm
package Watchdog;
use Moose::Role;
requires 'bark'; # will assert! evaluated before 'method' is processed
sub warn_intruder {
my $self = shift;
my $intruder = shift;
$self->bark until $intruder->gone;
}
1;
A workaround for this problem is to use "with" only after the methods
have been defined. To take our previous example,
Canine could be
reworked thus:
package Canine;
use Moose;
use MooseX::Method::Signatures;
method bark { print "Woof!\n"; }
with 'Watchdog';
1;
A better solution is to use MooseX::Declare instead of plain
MooseX::Method::Signatures. It defers application of roles until the end of
the class definition. With it, our example would becomes:
# in file Canine.pm
use MooseX::Declare;
class Canine with Watchdog {
method bark { print "Woof!\n"; }
}
1;
# in file Watchdog.pm
use MooseX::Declare;
role Watchdog {
requires 'bark';
method warn_intruder ( $intruder ) {
$self->bark until $intruder->gone;
}
}
1;
Subroutine redefined warnings
When composing a Moose::Role into a class that uses MooseX::Method::Signatures,
you may get a "Subroutine redefined" warning. This happens when both
the role and the class define a method/subroutine of the same name. (The way
roles work, the one defined in the class takes precedence.) To eliminate this
warning, make sure that your "with" declaration happens after any
method/subroutine declarations that may have the same name as a
method/subroutine within a role.
SEE ALSO¶
MooseX::Declare
Method::Signatures::Simple
Method::Signatures
Perl6::Subs
Devel::Declare
Parse::Method::Signatures
Moose
AUTHORS¶
- •
- Florian Ragwitz <rafl@debian.org>
- •
- Ash Berlin <ash@cpan.org>
- •
- Cory Watson <gphat@cpan.org>
- •
- Daniel Ruoso <daniel@ruoso.com>
- •
- Dave Rolsky <autarch@urth.org>
- •
- Hakim Cassimally <hakim.cassimally@gmail.com>
- •
- Jonathan Scott Duff <duff@pobox.com>
- •
- Justin Hunter <justin.d.hunter@gmail.com>
- •
- Kent Fredric <kentfredric@gmail.com>
- •
- Maik Hentsche <maik.hentsche@amd.com>
- •
- Matt Kraai <kraai@ftbfs.org>
- •
- Rhesa Rozendaal <rhesa@cpan.org>
- •
- Ricardo SIGNES <rjbs@cpan.org>
- •
- Steffen Schwigon <ss5@renormalist.net>
- •
- Yanick Champoux <yanick@babyl.dyndns.org>
- •
- Nicholas Perez <nperez@cpan.org>
- •
- Karen Etheridge <ether@cpan.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2012 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.