if a user with/without phone number are equally valid states to be then types won't help you much. I think it's more about writing

  class User{phone: ?PhoneNumber}

over

  class User{phone: ?string}.

▲ throwwwll 6 hours ago | parent [-]

To expand and give some notion of good taste:

It's more about writing

    struct User {phone: MaybePhoneNumber} // give or take, it's a monoid

over

    struct User {phone: Option<String>}

	▲	pillmillipedes 6 hours ago \| parent [-]
		I don't mind discussing syntax when appropriate, but this feels like arguing over which trivial brainfuck substitution[1] is the best. > monoid nullables with `??` and `?.` are also give-or-take monoids. is it common though to `or` two MaybePhoneNumbers together or to apply a PhoneNumber->MaybePhoneNumber function to it? if not then why mention it? let's see something meaningfully different like a database schema. [1] https://esolangs.org/wiki/Trivial_brainfuck_substitution