PHP File_MARC equality oddness

file_marc_equality.php

<?php // 5.3
// From: http://pear.php.net/package/File_MARC
require 'File/MARC.php';
// From: https://github.com/abelperez/php-commons
require '../lib/collections/SimpleIterator.php';
require '../lib/collections/Set.php';
require '../lib/collections/ArraySet.php';

// Create a datafield
$a = new File_MARC_Data_Field('245', null, 1, 0);
$a->appendSubfield(new File_MARC_Subfield('a', 'Hello, World! /'));
$a->appendSubfield(new File_MARC_Subfield('c', 'by Mark Cooper.'));
echo $a . '<br/>';
echo var_dump($a) . '<br/>';
// Create a datafield - like the API provided example
$b_subs = array(); # just to be extra cautious ...
$b_subs[] = new File_MARC_Subfield('a', 'Hello, World! /');
$b_subs[] = new File_MARC_Subfield('c', 'by Mark Cooper.');
$b = new File_MARC_Data_Field('245', $b_subs, 1, 0);
echo $b . '<br/>';
echo var_dump($b) . '<br/>';
# Equality testing has issues ...
// echo ($a == $b) ? 'The fields are equal<br/>' : 'The fields are unequal<br/>'; # breaks
echo ($a === $b) ? 'The fields are equal<br/>' : 'The fields are unequal<br/>'; # works

// Let's try the identical approach
$c = new File_MARC_Data_Field('245', null, 1, 0);
$c->appendSubfield(new File_MARC_Subfield('a', 'Hello, World! /'));
$c->appendSubfield(new File_MARC_Subfield('c', 'by Mark Cooper.'));
echo $c . '<br/>';
echo var_dump($c) . '<br/>';
// echo ($a == $c) ? 'The fields are equal<br/>' : 'The fields are unequal<br/>'; # still breaks ...

$records         = new File_MARC('sample.mrc');
$all_subjects    = array();
$unique_subjects = new ArraySet();

while($record = $records->next()) {
	foreach ($record->getFields('650') as $subject) {
		$all_subjects[] = $subject;
		// $unique_subjects->add($subject); # fails at in_array
		$unique_subjects->add($subject->__toString()); # works
	}
}

echo 'ALL: ' . count($all_subjects);
echo '<br/>';
echo 'UNQ: ' . $unique_subjects->size();
echo '<br/>';
$i = $unique_subjects->iterator();
$i->sort();
while($s = $i->next()) {
	echo $s . '<br/>';
}