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

[Sean Heber]

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.

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
> 
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