With all due respect -- as I'm sure that Moose is techinically excellent -- I don't really understand how it is really any different from a practical perspective than most of the other full-featured class system generators for Perl.

You define a syntax for users to create constructors, accessors, etc. You've got some clean syntax and some stronger type-checking than some class builders, true, but the basic concept of providing an interface to generate a class hasn't changed a lot since, say, Class::MethodMaker (which goes back to 1996).

With almost any full system, you get the accessors and constructors 'for free' and don't need to know the details. For example:

package Stopwatch;
use strict;
use warnings;
use DateTime;

use Class::MethodMaker [ 
  scalar => [ { -type => 'DateTime', -default_ctor => sub { DateTime->
+now },             
              'timer' ],
  new    => 'new',
];

sub diff {
    my $self = shift;
    $self->timer - DateTime->now;
}

# ...

my $sw = Stopwatch->new;
# ... wait a moment
print $sw->diff;
[download]

Only when you move away from using accessors to get at encapsulated data does the underlying form really matter. For example, with inside-out objects:

package Stopwatch;
use strict;
use warnings;
use DateTime;

use Class::InsideOut qw( public register id );

public timer => my %timer => {
  set_hook => { $_->isa('DateTime') or die "must be a DateTime object"
+ }
};

sub new {
  my $self = register( bless \(my $s) );
  $timer{ id $self } = DateTime->now;
  return $self;
}

sub diff {
    my $self = shift;
    $time{ id $self } - DateTime->now;
}

# ...

my $sw = Stopwatch->new;
# ... wait a moment
print $sw->diff;
[download]

Could you help me understand what's really different about Moose beyond syntax?

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