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My favorite Java code I've ever seen is:

    @Nullable Optional<Boolean> foo;

For when 3 values for a boolean just aren't enough.

Here are two rules I learned from data modelling and APIs many years ago:

1. If you don't do arithmetic on it, it's not a number. ID int columns and foreign keys are excluded from this. But a phone number or an SSN or a employee ID (that is visible to people) should never be a number; and

2. It's almost never a boolean. It's almost always an enum.

Enums are just better. You can't accidentally pass a strong enum into the wrong parameter. Enums can be extended. There's nothing more depressing than seeing:

    do_stuff(id, true, true, false, true, false, true);

This goes for returning success from a function too.

kelnos 4 days ago [ - ]

> @Nullable Optional<Boolean> foo;

To be (somewhat facetiously) fair, that's just JSON. The key can be not-present, present but null, or it can have a value. I usually use nested Options for that, not nulls, but it's still annoying to represent.

In Rust I could also do

    enum JsonValue<T> {
        Missing,
        Null,
        Present(T),
    }

But then I'd end up reinventing Option semantics, and would need to do a bunch of conversions when interacting with other stuff.