[swift-evolution] [swift-evolution-announce] [Rejected] SE-0097: Normalizing naming for "negative" attributes

[Matthew Johnson]

> On Jun 2, 2016, at 9:52 AM, Sean Heber via swift-evolution <swift-evolution at swift.org> wrote:
> 
> In terms of naming, I almost feel like “None” would be a better name for it as then it reads somewhat as the opposite of “Any” and that has a nice symmetry to me.

+ 1.  Although the inverse of “None” is really “All” (as in “all or none”).  I’m not necessarily suggesting we use “All”, just pointing out the linguistic relationship.  

That said, I do believe we should *consider* alternatives names for “Any” as part of the discussion of the name for a bottom type.  It would be nice symmetry if we found names for the top and bottom types that are inverses of each other.

> 
> l8r
> Sean
> 
> 
>> On Jun 2, 2016, at 4:04 AM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>>> 1) For noreturn, the core team prefers to explore a solution where a function can be declared as returning an non-constructable “bottom” type (e.g. an enum with zero cases).  This would lead to something like:
>>> 
>>> 	func abort() -> NoReturn { … }
>>> 
>>> This will require some new support in the compiler, but should flow better through the type system than @noreturn in function composition and other applications.  Joe Groff offered to write a proposal for this.
>> 
>> Are you thinking in terms of a *real* bottom type—that is, a type which is the subtype of all types—or a fake bottom type which is simply an empty enum?
>> 
>> If you're thinking about a real bottom type, I wouldn't want to call it `NoReturn`, because the bottom type may end up playing a larger role in the language. Given our use of `Any`, the natural names for a bottom type are probably `All` (as the subtype of all types) or `None` (as a type with no instances). I do worry that those names are a little too short and attractive, though. `None` might be mistaken for `Void`; `All` might be mistaken for `Any`, and wouldn't make much sense when read as the return value of a function.
>> 
>> My best suggestion is `Never`. A function with a `Never` return type would read as "never returns":
>> 
>> 	func abort() -> Never { … }
>> 
>> If it appeared in, say, a generic type, it would mean "never occurs":
>> 
>> 	let result: Result<String, Never>
>> 
>> Flowing from that, we can end up with functions taking a `Never` parameter, which are never called:
>> 
>> 	result.flatMapError { (_: Never) in fatalError("can't happen") }
>> 
>> Or `Never?` values, which are never `some`:
>> 
>> 	let _: Never? = Result<String, Never>.error
>> 
>> (By the way, the return type of the force unwrap operator on a `Never?` is `Never`, which is just right: if you force unwrap a `Never?`, it will always trap, never return.)
>> 
>> The main issue I see with `Never` is that it's an adverb, not a noun. But the nouns all seem to have problems. And besides, the bottom type isn't so much a thing as a lack of a thing, isn't it? That's bound to have a slightly funky name.
>> 
>> -- 
>> Brent Royal-Gordon
>> Architechies
>> 
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution