this post was submitted on 05 Sep 2024
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Programming
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The items don't seem concise and always clear. But seems like a good, inspiring resource for things to consider.
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.
This might be educational: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html
There are issues that the
Optionalclass 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
nullto be present: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining https://www.jetbrains.com/help/inspectopedia/OptionalToIf.htmlThis 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.
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
nullas a keyword.What does your reasoning mean in that context?
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
Nullvalue is usually worse than usingOptionor similar. Andnullptr_tdoesn't help with this at all.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.
C#'s
nullkeyword matches the monadic approach I mentioned earlier. Nullable types work as aMaybemonad. It's the same concept shoehorned differently due to the different paths taken by these languages.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.
Correct.
"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
Integerin Java, for example, are the boxed machine ints andnull. The inhabitants ofOptional[Integer](it won't let me use angle brackets here) areOptional.of(i)for each machine inti,Optional.empty(), andnull.Optional.empty()is not null and should not be called a "Null object." It's also not of typeInteger, 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 havenullat all, this is idiomatic.I think you're trying too hard to confuse yourself.