rkg has asked for the wisdom of the Perl Monks concerning the following question:

Hi --

I am planning on using Class::MethodMaker like this:

package Simple; use constant REQFIELDS => qw(a b); use Class::MethodMaker get_set => [REQFIELDS, qw(c d)], new_with_init => 'new', new_hash_init => 'hash_init'; sub init { my $self = shift; my %values = (@_); foreach (REQFIELDS) { die "$_ doesn't exist" unless exists($values{$_}); } $self->hash_init(%values); return; } 1;
The idea is the object must define certain attributes at creation. Rather than start each class with this idiom, I was thinking of subclassing Class::MethodMaker as per the docs so I could specify certain get_set methods as 'required', such that the class would die if an object was created lacking these arguments.

The docs on subclassing C:MM leave me somewhat befuddled... Can anyone give me some suggestions how might I subclass C:MM to obtain this 'required' method functionality?

Thanks for any suggestions


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Re: Subclassing Class::MethodMaker to obtain "required" fields
by rkg (Hermit) on Dec 15, 2003 at 04:27 UTC
    This seems to work. Posting it in case someone else finds it helpful.
    package MakeMethod; use strict; use base qw( Class::MethodMaker ); sub new_hash_init_required { my ($class, @args) = @_; my %methods; foreach (@args) { $methods{$_} = sub { my $class = shift; my $self = ref($class) ? $class : bless {}, $class; my %args = (scalar @_ == 1 and ref($_[0]) eq 'HASH') ? %{ +$_[0]} : @_; foreach (keys %args) { if (my $setter = $class->can(" __CMM__ $_")) { $setter->($self, $args{$_}); } else { $self->$_($args{$_}); } } die "must specify required" unless $self->can("required"); my @req = $self->required; foreach my $req (@req) { die "$req does not exist" unless exists($self->{$req}) +; } $self; }; } $class->install_methods(%methods); } sub required { my ($class, @req) = @_; my %methods; $methods{required} = sub { @req }; $class->get_set(@req); $class->install_methods(%methods); } 1;
    While I had trouble grasping the C:MM docs, reading the source made it much clearer.