Package spec as a PHP 5.3 closure?

.package.php

<?php

$package = function ($s) {
    $s->name = 'Overlord';
    $s->authors = 'Padraic Brady, Sauron[[email protected]]';
    $s->version = '0.0.1-dev';
    $s->api_version = '0.0.1-dev';
    $s->summary = 'Monitoring library for Hobbit Detector 1.0';
    $s->description = file_get_contents(__DIR__ . '/description.txt');
    $s->homepage = 'http://en.wikipedia.org/wiki/Sauron';
    $s->changelog = file_get_contents(__DIR__ . '/changelog.txt');
    $s->files->php[] = 'library/**/*.php';
    $s->files->tests[] = 'tests/**/*.*';
    $s->files->reject[] = '*.project';
    $s->files->bin[] = 'scripts/overlord.bat';
    $s->include_path = 'MutateMe/Mutations/';
    $s->dependencies[] = 'PHP[>=5.3.1]';
    $s->dependencies[] = 'Pear[>=1.6.5]';
    $s->dependencies[] = 'MutateMe[0.5.0]';
    $s->dependencies[] = 'ext/runkit';
    $s->optional_dependencies[] = 'ext/eyeofsauron';
    $s->license = 'New BSD';
};

No, not opposed to a stdClass. I'm rather trying to find out why it's necessary to have an "is-a" relationship by tagging $s (still not sure of what's being passed in) with a function, instead of a more compressed "has-a" relationship like

$package = new stdClass;
$package->name = 'Overlord';
...
$s->package = $package;