Comment on Java 21 makes me actually like Java again

PortugalSpaceMoon@infosec.pub ⁨1⁩ ⁨year⁩ ago

• BatmanAoD@programming.dev ⁨1⁩ ⁨year⁩ ago

  They allude to this later, acknowledging that it’s sort of a cross between unit and bottom.

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  • aloso@programming.dev ⁨1⁩ ⁨year⁩ ago

    No it’s not, it is 100% a unit type (except it’s not really a type, since you can only use it as return type and nowhere else)

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    • 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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