OO-Perl Aliasing Class Attributes

Question

I have a module that I'm working on. I am setting up a few attributes like this:

$self->{FOO};
$self->{BAR};
$self->{FOOBAR};

And, I want to use AUTOLOAD to help create methods for accessing these attributes. For example, $foo->Bar() returns the value of $self->{BAR}. No problem. Everything is standard.

Now, I want to create alias Methods. For example, if someone says $obj->Fu();, I'll return $self->{FOO}. What I'd like to do is create a $self->{FU} that points to the same memory location as $self->{FOO}. That way, when I set the value of $self->{FOO}, $self-{FU} is also set. This way, I don't have to make all sorts of changes in the way AUTOLOAD works or remember to set $self->{FU} whenever I set $self->{FOO}.

Any easy way of doing this?

Answer 1

Yes, use Moose, rather than attempting to make explicit mapping between hash keys. Writing your own accessors, or using AUTOLOAD, is not necessary and has a much higher chance of error:

package MyClass;

use Moose;
use MooseX::Aliases;

has foo => (
    is => 'rw', isa => 'Str',
    alias => 'fu',
);
has bar => (
    is => 'rw', isa => 'Str',
);
__PACKAGE__->meta->make_immutable;
no Moose;
1;

package main;
use strict;
use warnings;
use MyClass;
my $obj = MyClass->new;
$obj->foo("value");
$obj->fu("a new value");

# prints "foo has the value 'a new value'"
print "foo has the value '", $obj->foo, "'\n";

Answer 2

I would recommend Moose over what you're doing, but the easiest way to accomplish what you're asking is probably this:

sub Fu { shift->Foo(@_) }

This way, it doesn't matter if Foo is autoloaded or not.

Answer 3

The non-Moose solution is to just create an alias in the symbol table. It's not a common thing to do, and I suspect that whatever you are trying to do has a better way, Moose or otherwise. Don't use any of this if you can avoid it with a better design or interface, which are often the superior solutions to things like this.

In this AUTOLOAD routine, I look at a %Aliases hash to figure out other methods else I have to define. When I have aliases, I make proper aliases in the symbol table. It's a bit ugly, but it avoids adding another actual method in the call stack:

#!perl

use 5.010;

{
package SomeClass;
use Carp;
use vars qw($AUTOLOAD);

sub new {
    return bless { 
        map { $_, undef } qw(FOO BAR FOOBAR)
        }, $_[0];
    };

my %Aliases = (
    FOO => [ qw(fu) ],
    );

sub AUTOLOAD {
    our $method = $AUTOLOAD;
    $method =~ s/.*:://;

    carp "Autoloading $method";

    {
    no strict 'refs';
    *{"$method"} = sub { 
        @_ > 1 
                ? 
            $_[0]->{"\U$method"} = $_[1]
                :
            $_[0]->{"\U$method"}
        };

    foreach my $alias ( @{ $Aliases{"\U$method"} } ) {
        *{"$alias"} = *{"$method"};
        }

    goto &{"$method"};
    }

    }

sub DESTROY { 1 }
}

my $object = SomeClass->new;

$object->foo(5);

say "Foo is now ",   $object->foo;
say "Foo is now ",   $object->foo(9);
say "Fu is now ",    $object->fu;
say "Fu is set to ", $object->fu(17);
say "Foo is now ",   $object->foo;

Now foo and fu access the same thing:

Foo is now 5
Foo is now 9
Fu is now 9
Fu is set to 17
Foo is now 17