conventions for friend methods in Perl

Question

Perl doesn't support a friend relationship between objects, nor does it support private or protected methods. What is usually done for private methods is to prefix the name with an underscore. I occasionally have methods that I think of as friend methods. Meaning that I expect them to be used by a specific object, or an object with a specific responsibility, but I'm not sure if I should make that method public (meaning foo ) or private ( _foo ) or if there's a better convention? is there a convention for friend methods?

Answer 1

I'm not aware of any conventions or best practices for friend methods that the Perl community uses. If you felt the need to designate a prefix for these methods I don't see any real issue with it, but I don't see any advantage in it either. Personally I'd just make it a "public" method, without the underscore, and without any additional prefix.

Answer 2

If you really want to have Friend semantics you could do something like this:

package A;

use Data::Dumper;

sub _friend
{
   die "you are no friend of mine" unless caller(0)->isa(__PACKAGE__);
   my $self = shift;
   "friend";
}

package B;

use base 'A';

sub new
{
   bless {}, shift;
}

sub test_friend
{
shift->_friend;
}

package main;

$bob = new B;

print $bob->test_friend, "\n";

print $bob->_friend, "\n";

I named the method with an underscore so that Test::Pod will will not complain that it is not documented.

Answer 3

Perl does not, by itself, enforce private methods or attributes, no. In fact, Larry Wall was once quoted as saying:

Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun.

If you're using Moose (and if you aren't, you really, really should), you could put your method, which I'll call foo, into a role, say Fooable, that can be composed into more than one class, thus allowing foo to be a method in any class that does the Fooable role.

If you want true privacy, though, it looks as though MooseX::Privacy provides that, although I don't have any experience using it.