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Comment on Java 21 makes me actually like Java again

BatmanAoD@programming.dev ⁨1⁩ ⁨year⁩ ago

It’s not possible to instantiate or assign, which is more like a never type than a unit; and it is not possible to define new types with the same properties, which is also more like bottom than unit. But you’re right that it’s not actually a true never type since it can’t represent function divergence.

I think the truth is just that Java’s type system isn’t very mathematically disciplined.

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aloso@programming.dev ⁨1⁩ ⁨year⁩ ago
It’s not possible to instantiate or assign, which is more like a never type than a unit

Actually, this is because void is not a type, it is just a keyword, that is allowed only instead of the return type.

If it were a bottom type, that would mean that a method returning void must diverge, which is simply not true.

Also, even if it were a bottom type, it would be possible to write an “unreachable” method

void foo(void bottom) { return bottom; }

But it is not, because void isn’t a bottom type, it’s no type at all.
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- BatmanAoD@programming.dev ⁨1⁩ ⁨year⁩ ago
  The post has been edited; it looks like someone on reddit made essentially the same point. You’re right of course that void isn’t a true type in Java, but the post now also discusses Void, which I suppose just shows how void infects the type system despite not being a type.
  
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