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know the features of your language
(lemmy.world)
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this post was submitted on 08 Dec 2023
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How are we supposed to deal with null values though? It's an important concept that we can't eliminate without losing information and context about our data.
0 and "" (empty string/char) are very often not equivalent to null in my use cases and mean different things than it when I encounter them.
You could use special arbitrary values to indicate invalid data, but at that point you're just doing null with extra steps right?
I'm really lost as to how the concept isn't neccessary.
I’ll point to how many functional languages handle it. You create a type
Maybe a, whereacan be whatever type you wish. The maybe type can either beJust xorNothing, wherexis a value of typea(usually the result). You can’t access thexvalue throughMaybe: if you want to get the value inside theMaybe, you’ll have to handle both a case where we have a value(Just x) and don’t(Nothing). Alternatively, you could just pass this value through, “assuming” you have a value throughout, and return the result in anotherMaybe, where you’ll either return the result through aJustor aNothing. These are just some ways we can useMaybetypes to completely replace nulls. The biggest benefit is that it forces you to handle the case whereMaybeisNothing: with null, it’s easy to forget. Even in languages like Zig, theMaybetype is present, just hiding under a different guise.If this explanation didn’t really make sense, that’s fine, perhaps the Rust Book can explain it better. If you’re willing to get your hands dirty with a little bit of Rust, I find this guide to also be quite nice.
TLDR: The
Maybemonad is a much better alternative to nulls.Isn't a Maybe enum equivalent to just using a return value of, for example,
int | nullwith type warnings?Not quite, because the Maybe enum is neither int nor null, but it's own, third thing. So before you can do any operations with the return value, you need to handle both cases that could occur
Isn't that also true with compile-time type checking though? Eg. 0 + x where x is int|null would be detected? I don't have much experience here so I could be wrong but I can't think of a case where they're not equivalent
Most languages that let you do ambiguous return types don't do compile-time type checking, and vice versa. But if it's actually implemented that way, then it's logically equivalent, you're right. Still, I prefer having things explicit
Yeah it's nice to be able to see it
Yes it is
One alternative are monadic types like result or maybe, that can contain either a value or an error/no value.
you could take a look at what Rust is doing with the Option enum. Superficially it looks similar to using null, but it actually accomplishes something very different.
A function that classically would return a value, say an int, but sometimes returns null instead, becomes a function that returns an Option. This forces explicit handling of the two cases, namely Some(value) or None. This way, it is next to impossible to try to do an operation on a value that does not exist.