[swift-evolution] Remove nil and NilLiteralConvertible

[Brandon Knope]

In my other thread where this came up, my support is:
1. Removing NilLiteralConvertible conformance from Optional (apparently other people use this protocol?)
2. Introducing a new keyword that is sugar for .none

Would I like to remove nil and NilLiteralConvertible? Perhaps, but it seems that some people use them for other things and I would hate to take it away from them. 

My concerns come down to this:
- It looks like a pointer
- People learning Swift as their first language will go to other languages and expect “nil” to be safe. Swift seems to be mostly alone here: nil is safe whereas in most languages it is not safe to dereference a nil pointer
- It is not consistent with the Optional enum naming
- It is not as descriptive or expressive


Brandon

> On Jun 8, 2016, at 4:59 PM, Brandon Knope via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Is it really an implementation detail? It is very leaky if it is one because it is highly exposed to everyone.
> 
> Regardless of whether or not it is an implementation detail, nil does not adequately describe the “none” case it is trying to represent in my opinion
> 
> B
> 
> 
>> On Jun 8, 2016, at 4:56 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>> 
>> On Wed, Jun 8, 2016 at 3:52 PM, Brandon Knope <bknope at me.com <mailto:bknope at me.com>> wrote:
>> .none or a more appropriate keyword like “none” (imo)
>> 
>> 
>> My point is that `.none` exposes the underlying enum. The premise here is that the enum is an implementation detail. You'll notice that, currently, significant sugar and magic is devoted to allowing you to work with optionals without ever writing `.some` or `none`. For example, `if let x = ...` and friends allow you to avoid writing `if case .some(let x) = ...`, while you can write `return x` instead of `return .some(x)`. This was, IIUC, a deliberate choice to allow progressive disclosure of the language to learners. Renaming `nil` to `none` is a different proposal from Anton is proposing here.
>>  
>> Brandon
>> 
>>> On Jun 8, 2016, at 4:47 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org <mailto: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 <mailto: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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> 
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