this post was submitted on 05 Sep 2024
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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.
"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.