Python accessor example converted to Moose

accessor.pl

{
    package AnotherPerson;
    use Moose;
    use namespace::autoclean;
    
    has _firstname => (is => 'rw', isa => 'Str', accessor => 'firstname');
    has _lastname  => (is => 'rw', isa => 'Str', accessor => 'lastname' );
}

my $you = AnotherPerson->new;
$you->firstname('David');
$you->lastname('Mertens');



# 
# Stackoverflow answer: http://stackoverflow.com/a/9187853/12195
#

__END__

# orig Python example

class AnotherPerson:
    def __init__(self):
        self._firstname = None
        self._lastname = None

    @property
    def firstname(self):
        return self._firstname

    @firstname.setter
    def firstname(self, newname):
        self._firstname = newname

    @property
    def lastname(self):
        return self._lastname

    @lastname.setter
    def lastname(self, newname):
        self._lastname = newname

you = AnotherPerson()
you.firstname = 'David'  # These two lines call instance methods
you.lastname = 'Mertens'

Apart from showing how this is done in Moose (in comparison to the Python example) I don't think this is of much real use in day2day stuff.

The example just shows you you can define an "internal" attribute with a different setter/getter method. However you can still get to attribute because Moose still boils down to being a hash based OO. For eg. $you->{_firstname}

Remember in Moose getter & setters are just method calls:

$you->firstname('David');      # setter

$you->firstname;               # getter

To get the...

$you->firstname = 'David';

... would require setting the lvalue on the method. Moose doesn't do this. However it hasn't stopped someone adding it has a MooseX extension :) See http://p3rl.org/MooseX::Meta::Attribute::Lvalue

Yes, but now for something on the crazy side. Is there a way to write a Perl method (with or without moose) such that you could say:

$object->name = 'David';

and have it execute a validation method for you? The first thought is, sure, you could do this by returning a tied scalar; then, by overriding the STORE method, you could have validation code. However, what if your attribute is an object? In that case, tying a scalar would solve the assignment issue, but would break standard method chaining like

my $width = $window->page_widget->width;

If the page widget returns a tied scalar, you won't be able to call a method on it because tied scalars do not support method calls. In this case, however, (and this is where I'm stretching it), you could use Damian's Contextual::Return. In lvalue context, return the tied scalar with a validation method. In any other context, return the object (or whatever sort of value that would be appropriate).

No, wait, even better, just use Want: https://metacpan.org/module/Want

Alright, see this gist: https://gist.github.com/1790290

There are some Perl modules already on CPAN which do provide lvalue accessors.....

• https://metacpan.org/module/Object::Accessor
• https://metacpan.org/module/Class::Accessor::Lvalue
• https://metacpan.org/module/Object::props
• https://metacpan.org/module/methods

I've never tried any of these so YMMV.