I've used the approach where every set of parameters has its own class. 

use Attribute::Property;

{
    package Param::function;
    sub new : New;

    # XXX - Both need anchors?
    sub type  : Property { /Order|Return/ }
    sub month : Property { grep /$_[1]/, 1 .. 12 }
}
sub function { 
    my $self = shift;
    ...
}

[download]
After which you can do 
my %params = (
    type  => qr/Order|Return/,
    month => sub { my $month = shift; return grep { /$month/ } (1 .. 1
+2) }
);
my $param = Param::function->new(\%params);

$param->type = 'Return';
$param->month = 3;

print $param->type;  # prints 'Return'
print $param->month; # prints 3

# the following two method calls will fail (croaking)
$param->type = 'Ovid';
$param->month = 13;

[download]
But I dislike param objects. The idea is great, but it's too much work in practice. Not because I created many classes, but because it's just too much work to create objects every time you want to pass parameters. I ended up using 
my $param = @_ == 1 ? shift : Param::function->new({ @_ });

[download]
everywhere and not actually using the parameter classes.

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

In reply to Re: RFC - Parameter Objects by Juerd
in thread RFC - Parameter Objects by Ovid

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