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submitted 2 months ago by lysdexic to c/programming

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[–] Kissaki 10 points 2 months ago* (last edited 2 months ago) (3 children)

The items don't seem concise and always clear. But seems like a good, inspiring resource for things to consider.

If it is expected that a method might fail, then it should fail, either by throwing an Exception or, if not - it should return a special case None/Null type object of the desired class (following the Null Object Pattern), not null itself.

I've never heard of evading null with a Null object. Seems like a bad idea to me. Maybe it could work in some language, but generally I would say prefer result typing. Introducing a result type wrapping or extending the result value type is complexity I would be very evasive to introduce if the language doesn't already support result wrapper/state types.

[–] [email protected] 2 points 2 months ago

This might be educational: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html

There are issues that the Optional class alleviates that are common enough to be documented: https://www.jetbrains.com/help/inspectopedia/ConditionalCanBeOptional.html (more detail is available at places like https://github.com/JetBrains/intellij-community/blob/a2d32ec64ed0fb37c7cc97856aa94cce95b17ee5/java/java-impl/src/inspectionDescriptions/ConditionalCanBeOptional.html (I believe this information used to be visible with the "inspectopedia" URLs but I don't see that today))

On the other hand, it seems there are some features / situations that require null to be present: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining https://www.jetbrains.com/help/inspectopedia/OptionalToIf.html

[–] lysdexic 2 points 2 months ago (2 children)

I’ve never heard of evading null with a Null object.

This is quite standard, and in fact it's even a safety feature. C++ introduced nullptr defined as an instance of std::nullptr_t explicitly with this in mind.

https://en.cppreference.com/w/cpp/language/nullptr

This approach is also quite basic in monadic types.

[–] Kissaki 4 points 2 months ago* (last edited 2 months ago) (2 children)

with this in mind

With what in mind? Evading NULL?

Languages that make use of references rather than pointers don't have this Dualism. C# has nullable references and nullability analysis, and null as a keyword.

What does your reasoning mean in that context?

[–] FizzyOrange 5 points 2 months ago* (last edited 2 months ago) (1 children)

Languages that make use of references rather than pointers don’t have this Dualism.

It's not about references vs pointers. You could easily have a language that allowed "null references" (edit: too much C++; of course many languages allow null references, e.g. Javascript) or one that properly separated null pointers out in the type system.

I agree with your point though, using a special Null value is usually worse than using Option or similar. And nullptr_t doesn't help with this at all.

[–] lysdexic 0 points 2 months ago (1 children)

With what in mind? Evading NULL?

Depends on your perspective. It's convenient to lean on type checking to avoid a whole class of bugs. You can see this either as avoiding NULL or use your type system to flag misuses.

Languages that make use of references rather than pointers don’t have this Dualism. C# has nullable references and nullability analysis, and null as a keyword.

C#'s null keyword matches the monadic approach I mentioned earlier. Nullable types work as a Maybe monad. It's the same concept shoehorned differently due to the different paths taken by these languages.

[–] [email protected] 1 points 2 months ago* (last edited 2 months ago) (1 children)

as far as I know, C# don't have proper ergonomic monadic bind as in F# (computation expression), Haskell (do expression), and Ocaml (let*), but I could be wrong.

[–] [email protected] 1 points 2 months ago

Correct.

[–] [email protected] 1 points 2 months ago* (last edited 2 months ago) (1 children)

"Monadic type" has something like three meanings depending on context, and it's not clear which one you mean. One of them is common in math, but not so common in programming, so probably not that. But neither "parametric types with a single argument" nor "types that encode a category-theoretic monad" have the property you say, as far as I know.

I imagine you're probably referring to the latter, since the optional monad exists. That's very different from returning null. The inhabitants of Integer in Java, for example, are the boxed machine ints and null. The inhabitants of Optional[Integer] (it won't let me use angle brackets here) are Optional.of(i) for each machine int i, Optional.empty(), and null.

Optional.empty() is not null and should not be called a "Null object." It's also not of type Integer, so you're not even allowed to return it unless the function type explicitly says so. Writing such function types is pretty uncommon to do in java programs but it's more normal in kotlin. In languages like Haskell, which don't have null at all, this is idiomatic.

[–] lysdexic -2 points 2 months ago (1 children)

I think you're trying too hard to confuse yourself.