Why are you checking the result of serialize here?

because of using ===

$b1 = new Binary(hex2bin('0c103357380648c9a84b867dcb625cfb'), Binary::TYPE_UUID);
$b2 = new Binary(hex2bin('0c103357380648c9a84b867dcb625cfb'), Binary::TYPE_UUID);
$b1 === $b2; //false
serialize($b1) === serialize($b2); //true

Yeah, that's what I suspected. Using serialize is not the right way to go about this. See my comment above about using == when comparing objects. Strictly speaking you should be comparing the BSON representation, but since that's not always easily possible I think a loose object comparison (which will leverage a class' compare_objects handler) is a safe middle ground.

Sorry, not sure I understood correctly, but why serialization is not right way here, can you explain a bit more, pls.
Example from your previous thread works correct. I guess there is even possible to leave just serialization. This example also working correctly:

$d1 = new Int64(12);
$d2 = new Int64(12);
$d1 === $d2; //false
serialize($d1) === serialize($d2); //true

=== is an identity check, meaning that values have to be identical. For scalar values this works fine, but it breaks down for objects as PHP will compare the internal object IDs as you've shown in the previous example.
== is an equality check, meaning there is some advanced comparison logic happening for objects. For objects that have a compare_objects handler implemented (which can only be done for internal classes such as MongoDB\BSON\Binary, it will call the first handler it finds (first checking the object on the left side of the operation, then that on the right) and return that result. If there is no compare_objects handler, it falls back to a property equality check for objects of the same class and returns false when the objects are of different classes.

This equality check is what we want here -- loosely speaking, when two values are equal (ignoring PHP's type coercion shenanigans around numeric strings) we can assume that they will map to the same representation in the database. serialize is an unnecessary complication at that point.

The theory of differences ==/=== i know but with all due respect to your work and your knowledge, I cannot agree with you that serialize is unnecessary complication. What you described much more complicate for me... at first check both values is scalar or no, next compare this values by ===. If it's not scalar - compare objects == . In most cases first compare will work. As I said before the easiest way here - leave just serialization (even remove first if) which will work as expected for all types. Also comparing objects trough serialization is giving us feature to affect compare behaviour (not sure how it can be used :D).
It's just my thought, you're deciding is it respond your repo paradigm or no 🤝

@alcaeus I left comparing just by serialization. I faced an issue with comparing after castAttribute. The root in Laravel here. When I'm getting result from castAttribute the result the same for $original and for $attribute in every cases.

Could you elaborate on the issue you're facing? I'm not super sure what you mean.

I replaced your comparison with this and your test case was green

if ($this->isClassCastable($key)) {
 return match (gettype($attribute)) {
 'object' => $attribute == $original,
 default => $attribute === $original,
 };
}

Also doesn't seem to complicate things, unless I'm missing something. I agree with @alcaeus that serializing doesn't seem right here.

@paulinevos hello,
when I'm using serialization - it works for all variable types, without additional type definition and different comparing type.
Additionally I don't really like to use NOT strict comparing.

For this PR I changed usage to check variable type.

@paulinevos hello, when I'm using serialization - it works for all variable types, without additional type definition and different comparing type. Additionally I don't really like to use NOT strict comparing.

For this PR I changed usage to check variable type.

<?php
$id1 = new MongoDB\BSON\ObjectId("5c1a924c117c260dcf99cfa9");
$id2 = new MongoDB\BSON\ObjectId("5c1a924c117c260dcf99cfa9");
// Compare using strict equality
var_dump($id1 === $id2); // ❌ false
// Compare using loose equality
var_dump($id1 == $id2); // ✅ true
// Compare using string cast
var_dump((string) $id1 === (string) $id2); // ✅ true