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Void is not a good example for you to point out. Rust's interpretation is correct: The unit type () is what most functions should return. The void type has no v

by nayuki 3y ago

Void is not a good example for you to point out. Rust's interpretation is correct: The unit type () is what most functions should return. The void type has no valid values at all, which means it cannot be returned. It is other languages that are wrong for using the term void. The actual void in Rust is called never: https://doc.rust-lang.org/std/primitive.never.html https://doc.rust-lang.org/std/primitive.never.html .

saurik 3y ago
> The void type has no valid values at all, which means it cannot be returned. In C/C++, any value can be cast to void, which should be sensible as any pointer can decay to a pointer to void. Thereby, the Wikipedia definition of the void type even says it is like a unit type, and the page for the unit type notes 1) the void keyword simulates a unit type and 2) that--and I think this is very important, to get into the mindset of this term--that the actual unit object type in Java is named Void. It does really really suck that you can't declare a variable of type void and that some compilers decided the size was 1 for long enough that the size is now undefined (instead of 0), as these mistakes lead to a ton of ridiculous code duplication in C++ templates. (This would be the first thing on my list of things to fix if I were allowed to make any arbitrary breaking change to C++.) But like, it seems very wrong to claim it has no values at all: in C++, if you have a function that returns void, you can even call another function that returns void and use the return keyword oh whatever you consider it to have returned. It clearly has some kind of value in many contexts--and, despite having a size that is undefined (and potentially 1), that value carries no state--so there is only one possible value: it is merely the term people use for unit in this kind of language. (To be clear, though: I am not at all claiming that Rust is wrong for using () or unit or whatever, as there is a ton of history of using such in other safe academic languages and it certainly doesn't confuse someone like me. I do, though, think that its mission isn't well served by not at least trying to look as much like the specific languages that need to be replaced--C and C++--as possible.)

by nayuki 3y ago

saurik 3y ago

> The void type has no valid values at all, which means it cannot be returned. In C/C++, any value can be cast to void, which should be sensible as any pointer can decay to a pointer to void. Thereby, the Wikipedia definition of the void type even says it is like a unit type, and the page for the unit type notes 1) the void keyword simulates a unit type and 2) that--and I think this is very important, to get into the mindset of this term--that the actual unit object type in Java is named Void. It does really really suck that you can't declare a variable of type void and that some compilers decided the size was 1 for long enough that the size is now undefined (instead of 0), as these mistakes lead to a ton of ridiculous code duplication in C++ templates. (This would be the first thing on my list of things to fix if I were allowed to make any arbitrary breaking change to C++.) But like, it seems very wrong to claim it has no values at all: in C++, if you have a function that returns void, you can even call another function that returns void and use the return keyword oh whatever you consider it to have returned. It clearly has some kind of value in many contexts--and, despite having a size that is undefined (and potentially 1), that value carries no state--so there is only one possible value: it is merely the term people use for unit in this kind of language. (To be clear, though: I am not at all claiming that Rust is wrong for using () or unit or whatever, as there is a ton of history of using such in other safe academic languages and it certainly doesn't confuse someone like me. I do, though, think that its mission isn't well served by not at least trying to look as much like the specific languages that need to be replaced--C and C++--as possible.)