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Comment by w23j | Hacker News Reader

At least one of the values of Optional is to communicate in the API that a value can be missing. The article mentions that:

A programmer looking at the code for the first time will know, just by looking at the return type, "Hey, this method may not return a record! I'll have to handle that scenario."

Making this clear to users of an API is something that nullable properties can not do. The user has to deliberately ignore the fact that the value might be missing by calling `.get()`.

This looks like a advantage to me, so to say that Option does not solve ANYTHING seems incorrect. It certainly does not solve EVERYTHING.

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> A programmer looking at the code for the first time will know, just by looking at the return type, "Hey, this method may not return a record! I'll have to handle that scenario."

Well, that's basically the same thing with any nullable return then. Wether I return T or Optional<T>, there might be no record.

Even worse, when I return T, you only have 2 cases : I return something, or I return null.

With optional, you have 3 cases to check : I returned Something, I returned Optional.of(null), or I returned null.

You should never have to check that the Optional itself is null. While that is allowed by the language, it is such an obvious error that static analysis tools could easily detect it.

Then it shouldn't be allowed by the language, and that's the core issue. Until the compiler enforces that Optionals aren't null they're not fit for most purposes.

I am not sure I understand.

I guess you are either saying (A) to treat every return type as possibly null or (B) to use your judgment when doing null checks of return types.

In case of (A): Do you want to write null-checks for methods like String.toUpperCase() or for user.getLastName()? That would lead to a lot of bloated, dead code. Also do you want to write error handling for all these cases you know can never happen?

In case of (B): NullPointerExceptions are most likely when the user of an API did not expect he might get a null value. For instance user.getDepartment -> null. "What? An employee does not have to have a department?!" In this case you force users of an API to guess if they might reive a null return value. And they might guess wrong, which either leads to dead code or NPEs. Using Optional as a return type makes the difference explicit.

I would say that every return type that can be NULL should be checked for being NULL. In C++, this is possible, because you most functions are return-by-value or return-by-reference. This leaves only return-by-pointer that need to be explicitly checked. In Java, all functions that do not return primitives are return-by-pointer, and are therefore nullable. This, as you mentioned, makes it infeasible to apply null-checks on every function return.

A consistent API written with Optional should make it such that if an Optional is returned, then a null value could have been returned. If an Optional is not returned (including for references), then you can assume that null will not be returned. This is a contract that can be documented as part of the API documentation.

To me, this is much clearer than having to guess on every call and I would prefer this use of Optional or not in an API to an API without Optional and having to check everything.

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