A few nodes dealing with attribute issues over the last little while prompted me to learn a little about this rather under used feature of Perl. A need to validate parameter lists to object constructors and option setting members inspired me to rope attributes into the task. Consider:

package Entity;

use strict;
use warnings;

my %okParams;
my %paramBase;

sub FETCH_CODE_ATTRIBUTES {
    my ($package, $referrent) = @_;
    return () unless exists $paramBase{$package};
    return @{$paramBase{$package}}[1 .. $#{$paramBase{$package}}];
}

sub MODIFY_CODE_ATTRIBUTES {
    my ($package, $referrent, @attrs) = @_;

    @attrs = map {"-$_"} @attrs;
    $okParams{$_} = $package for @attrs;
    $paramBase{$package} = \@attrs;
    return ();
}

sub new: Id {
    my ($class, %params) = @_;
    my %self;
    
    @self{keys %okParams} = @params{keys %okParams};
    
    my @badParams = grep {! exists $self{$_}} keys %params;
    
    warn "Class $class doesn't accept the following parameters: @badPa
+rams"
        if @badParams;
        
    return bless \%self, $class;
}

1;

package Member;

use base qw(Entity);

sub new: Name Nick Age Gender {
    my ($class, %params) = @_;
    
    return Entity::new ($class, %params);
}

1;

package main;

my $member = Member->new (-Name => 'fred', -Id => 1, -Wibble => 1);
[download]

generates the warning:

Class Member doesn't accept the following parameters: -Wibble at nonam
+e.pl line 42.
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