[swift-evolution] Remove nil and NilLiteralConvertible

[Brandon Knope]

1. People will find .none ugly which is why I think it could be replaced by a none keyword. It is awkward
2. none is more descriptive than nil in this case. The case is named none (consistency!) and nil is a holdover from other languages

I understand how nil works in the context of other languages. But looking at Optional:
public enum Optional<Wrapped> : NilLiteralConvertible {

    /// The absence of a value.
    ///
    /// In code, the absence of a value is typically written using the `nil`
    /// literal rather than the explicit `.none` enumeration case.
    case none

    /// The presence of a value, stored as `Wrapped`.
    case some(Wrapped)
}


These are not pointers and they sure look like one when you assign nil to an optional

B

Why would nil be chosen to represent the none case in the absence of other languages?


> On Jun 8, 2016, at 4:55 PM, Sean Heber <sean at fifthace.com> wrote:
> 
> If you add a new keyword called “none” without the period, but keep allowing “.none” to work because Optional is really an enum… then I don’t really see what has been gained here at all - you’re basically back to nil/.none => 2 ways to say the same thing!
> 
> l8r
> Sean
> 
> 
>> On Jun 8, 2016, at 3:52 PM, Brandon Knope via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> .none or a more appropriate keyword like “none” (imo)
>> 
>> Brandon
>> 
>>> On Jun 8, 2016, at 4:47 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> It's been pointed out before that Optional being an enum type is treated like an implementation detail. Currently, it is possible to teach the concept of Optional without introducing enum types or generics. How would you do so after elimination of nil?
>>> 
>>> 
>>> On Wed, Jun 8, 2016 at 3:41 PM, Антон Жилин <swift-evolution at swift.org> wrote:
>>> (No joking)
>>> Points:
>>> 
>>> 1. When nil was added to the language, we could not infer enumeration type:
>>> if x != Optional.none { ... }
>>> 
>>> Now it looks like this:
>>> if x != .none { ... }
>>> 
>>> If at this point we had a proposal to add nil as a replacement for .none, would we accept it?
>>> 
>>> 2. nil is very generic, it only approximately allows to express the intentions.
>>> In case of Optional, .none is clearer. In case of JSON processing, .null is clearer. In case of a semantically nullable struct, NilLiteralConvertible usually goes to default constructor.
>>> 
>>> 3. Too many "empty" things: .none, nil; NSNull, Void, NoReturn types.
>>> 
>>> 4. There should be a single consistent terminology: no value in Swift equals none.
>>> 
>>> - Anton
>>> 
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