How many options fit into a boolean?

Posted by luu 3 days ago

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Comments

Comment by ralferoo 9 hours ago

True | False | FileNotFound was a meme about 2 decades ago, and even that was a reference to MSDOS from another 2 decades earlier. I guess things never change, only the language.

Even now, I still find myself using true/false/null on occasions, but I'm usually smart enough to replace it with an enum at that point. The only time I don't is when it's an optional parameter to a function to override some default/existing value, at which point it then makes sense to keep it as an optional bool.

Comment by hinkley 9 hours ago

I did a govt contract early on and learned that yes/no/unanswered/unasked was a common quad. I see that in disclosures when applying for jobs as well.

Comment by nine_k 4 hours ago

This just means that the problem requires more than a Boolean, but rather something like boolean | error. In many languages from the OOP heyday that alternative part was expressed via throwing an exception.

Comment by gizmo686 9 hours ago

I'm surprised that trinary logic has not become a standard part of standard libraries yet. Almost every project I have worked on ends up with some form of a yes/no/maybe abstraction.

Comment by hinkley 9 hours ago

With privacy coming back into vogue, it’s useful to distinguish “we didn’t ask” from “they wouldn’t answer”

For some vector logic the distinction could matter.

Comment by Aurornis 8 hours ago

Yes/No/Maybe is a good fit for an enum because “Maybe” carries some specific information.

For more common situations where the yes/no bool is not available yet or should not be considered, constructs like Rust’s Option<bool> are a very good fit. Layering the bool inside of an Option creates intentional handling about the presence or lack of value first before you can work with it.

Comment by gima 7 hours ago

"How many options fit into a boolean?" Five or two, according* to Microsoft.

> MsoTrioState is "a tri-state Boolean value". it has five possible values. only two of them are supported.

*) https://learn.microsoft.com/en-au/dotnet/api/microsoft.offic...

Sourced from here https://fedi.lynnesbian.space/@lynnesbian/115969259564305759

Comment by rf15 7 hours ago

Funnily enough that was also my first idea upon reading the headline.

So let's remember: some programmer, somewhere, is right now thinking about building a tri-state boolean because they think it fits their current problem perfectly fine. And they are always wrong.

Comment by gizmo686 7 hours ago

I've implemented trits a bunch of times and have never regretted it.

How you get 5 possible values into a tri state Boolean is beyond me though.

Comment by pavon 10 hours ago

Neat. Even knowing about niche optimization I would have guessed that you could fit 7 Options - one bit for each. But the developers were smart enough to take advantage of the fact that you can't have a Some nested below a None, so you only need to represent how many Somes there are before you reach None (or the data), allowing 254 possibilities.

Comment by gizmo686 9 hours ago

I doubt they were thinking about Option<bool> when making niches work like this.

Option<NonZeroU32> seems like a much more reasonable to justify this with. Also, enums can easily have invalid bit patterns that are unused without there being any specific bit that is always available. All you need is a single variant of the enum to have a free bit, and you have a niche to shove None into.

Comment by gizmo686 9 hours ago

It's not clear from the article, but "niche optimization" does not mean "optimization that is only useful in a very specific circumstance".

It is a specific optimization based on the idea of storing one type inside of another type by finding a "niche" of unused bit pattern(s) inside the second type.

It has far more useful application than a tower of Option 254 deep.

Comment by nine_k 10 hours ago

The scoop: a boolean can't be smaller than a byte. Full 254 level of nested Option<bool> fit into it. (C++ needs much more for even a single level.)

Comment by shagie 9 hours ago

For Java developers... you can use Optional<Boolean> to store the elusive four possible booleans.

Comment by nitnelave 8 hours ago

5, no? Null, Optional::empty, Optional(null), Optional(true), Optional(false)

Comment by shagie 8 hours ago

    public static void main (String[] args) {
        Optional<Boolean> n = Optional.ofNullable(null);
        Optional<Boolean> e = Optional.empty();
        System.out.println(n.equals(e));
    }

    true
https://ideone.com/EGRdi5

A null in an Optional is empty. So you've got:

    Optional<Boolean> n = null;
    Optional<Boolean> e = Optional.empty();
    Optional<Boolean> t = Optional.of(Boolean.TRUE);
    Optional<Boolean> f = Optional.of(Boolean.FALSE);

Comment by priowise 10 hours ago

This question always reminds me that we often compress far more nuance into binary decisions than reality allows. In practice most systems end up inventing “soft booleans” (flags, states, priorities) to deal with that.

Comment by vadelfe 9 hours ago

The deeper you go into memory layout, the more you realize that even "simple" types aren't that simple.

Comment by RobotToaster 9 hours ago

>and that it takes up one byte of memory

You can make them smaller using bitfields in C.

Comment by AlotOfReading 9 hours ago

The object it's inside will still take up at least one byte.

    sizeof(struct {bool a:1;}) == sizeof(char);

Comment by hinkley 9 hours ago

Amortization.

If one Boolean must be a byte then 8 must be eight bytes. Which is not true. A boolean can be 1/8th of a byte which is a meaningful distinction.

Comment by hinkley 6 hours ago

3^5 is 243 so one could also call an optional Boolean 1/5th of a byte, though 1/4 is so much simpler to read and write.

Comment by gottheUIblues 2 hours ago

A trit is log(3)/(8log(2))=0.19812031259014 of a byte

Comment by russdill 9 hours ago

Um, no. Please show me how you can fit 255 possible states in something smaller than a byte by using bitfields.

Comment by RobotToaster 9 hours ago

I was quoting the first paragraph, where it says a single normal bool takes a byte.

Comment by mock-possum 10 hours ago

> looking at Rust … it turns out that `Option<bool>` takes up exactly one byte of memory, the same as bool! The same is true for `Option<Option<bool>>`, all the way up to 254 nested options.

Ah how many of those options fit into that boolean. Word games!