Fix wrong data type in codec tutorial

[alcaeus]

As is, the example would cause a type error. Thanks @OskarStark for bringing this to our attention!

[GromNaN]

@alcaeus the phpcs job should run on this PHP file.

[OskarStark]

Should it be renamed then?

- DateTimeCodec
- DateTimeImmutableCodec

[GromNaN]

Should it be renamed then?

- DateTimeCodec
- DateTimeImmutableCodec

Immutability should be the default and DateTime should be prohibed. The codec name seems correct. It could be more permissive and accept any DateTimeInterface, but always output a DateTimeImmutable.

[OskarStark]

Well if I have to deal with external objects which are using DateTime, I would end up having a DateTimeCodec and a DateTimeImmuatableCodec. I agree that immutability is recommended and would always use it, but maybe I am not in charge of this 🤷‍♂️

[GromNaN]

It's a tutorial, I like that it teaches good practices more broadly than the subject covered.

[OskarStark]

I totally agree, but would change the name anyway to DateTimeImmutable, but its not my decision

[alcaeus]

the phpcs job should run on this PHP file.

I deferred this on purpose so that I can use PHP 8.1 syntax in the codec tutorial. If we want to run phpcs, I'll have to change it back to PHP 7.4 syntax.

I decided to ignore the naming discussion as this is just supposed to be inspiration for people. I did however add a note about the codec accepting any DateTimeInterface when encoding to BSON but always decoding to DateTimeImmutable.

[OskarStark]

❤️