Comment on Java 21 makes me actually like Java again

PortugalSpaceMoon@infosec.pub ⁨11⁩ ⁨months⁩ ago

• BatmanAoD@programming.dev ⁨11⁩ ⁨months⁩ ago

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

  source

  • aloso@programming.dev ⁨11⁩ ⁨months⁩ 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)

    source

    • BatmanAoD@programming.dev ⁨11⁩ ⁨months⁩ 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.

      source

      • aloso@programming.dev ⁨11⁩ ⁨months⁩ 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.

        source

        • -> View More Comments