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.
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, a placeholder used instead of the return type when a function doesn’t return anything.
If it were a bottom type, that would mean that a method returning void must diverge, which is simply not true.
Also, if it were a bottom type, it would be possible to write an “unreachable” method
void unreachable(void bottom) {
return bottom;
}
Even though it couldn’t be called, it should be possible to define it, if void was a bottom type. But it is not, because void isn’t a bottom type, it’s no type at all.
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.
You are not logged in. However you can subscribe from another Fediverse account, for example Lemmy or Mastodon. To do this, paste the following into the search field of your instance: !programming@programming.dev
Welcome to the main community in programming.dev! Feel free to post anything relating to programming here!
Cross posting is strongly encouraged in the instance. If you feel your post or another person’s post makes sense in another community cross post into it.
Hope you enjoy the instance!
Rules
Rules
Follow the programming.dev instance rules
Keep content related to programming in some way
If you’re posting long videos try to add in some form of tldr for those who don’t want to watch videos
They allude to this later, acknowledging that it’s sort of a cross between unit and bottom.
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)
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.
Actually, this is because
voidis not a type, it is just a keyword, a placeholder used instead of the return type when a function doesn’t return anything.If it were a bottom type, that would mean that a method returning
voidmust diverge, which is simply not true.Also, if it were a bottom type, it would be possible to write an “unreachable” method
Even though it couldn’t be called, it should be possible to define it, if
voidwas a bottom type. But it is not, becausevoidisn’t a bottom type, it’s no type at all.The post has been edited; it looks like someone on reddit made essentially the same point. You’re right of course that
voidisn’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.