Currently, “nil” can mean either “uninitialized” or “initialized to nil”, which can be confusing. What I propose is cleaner and eliminates the need for implicitly unwrapped optionals.
`nil` always means “initialized to nil”. It never means “uninitialized”.
The point is that “nil" doesn’t capture the programmer’s intent precisely. The intent could be to delay initialization (e.g., until viewDidLoad) or it could be to use nil as a special value (e.g., to indicate the end of a linked list).
···
On Jan 7, 2016, at 7:09 PM, Jack Lawrence <jackl@apple.com> wrote:
As I mentioned elsewhere, you could still use “!” in the type to indicate a variable that may be uninitialized but is not necessarily an optional, thus separating the concepts of uninitialized from “initialized to nil”.
I’d be interested to see a real world code example where this language change is useful and as safe or safer than Optional/IUO.
Jack
On Jan 7, 2016, at 4:03 PM, Amir Michail via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
On Jan 7, 2016, at 6:58 PM, Jarod Long <swift@lng.la <mailto:swift@lng.la>> wrote:
The problem as I see it is that the functionality of none is already covered by optionals in a safer way. If something might be uninitialized, it really should be made explicit to the programmer so that they know to handle it properly. Implicitly-unwrapped optionals are already pretty generous in terms of allowing the programmer to ignore the possibility of a nil value, so it seems unnecessary to create a new feature to make it even easier.
Currently, “nil” can mean either “uninitialized” or “initialized to nil”, which can be confusing. What I propose is cleaner and eliminates the need for implicitly unwrapped optionals.
As I mentioned elsewhere, you could still use “!” in the type to indicate a variable that may be uninitialized but is not necessarily an optional, thus separating the concepts of uninitialized from “initialized to nil”.
Jarod
On Jan 7, 2016, 15:44 -0800, Amir Michail <a.michail@me.com <mailto:a.michail@me.com>>, wrote:
On Jan 7, 2016, at 3:15 PM, Jarod Long <jrd@lng.la <mailto:jrd@lng.la>> wrote:
None is really just another way of saying something is nil, and a type suffix to allow assigning none is exactly equivalent to implicitly-unwrapped optionals, so I don't see any value in replacing them with this feature.
“None" means a variable is uninitialized. “Nil" need not mean that.
Reading an uninitialized variable is an error. Reading a nil variable need not be.
With “none", you can have uninitialized variables without resorting to optionals or implicitly unwrapped optionals.
Not requiring a type suffix to assign none would be equivalent to allowing assignment of nil to any type, making everything an implicitly-unwrapped optional. You lose the compile-time nil safety that optionals provide, and the compiler likely loses many optimization opportunities because there are many situations where it can't know (or it is very difficult to know) whether a value could have possibly been assigned none at some point.
I understand the desire to reduce optionality to make code cleaner, but this kind of feature actually hides complexity and makes things more difficult in the long run. Implicitly-unwrapped optionals are a good compromise between cleanliness and effectively communicating when something can fail at run time.
Jarod
On Jan 7, 2016, at 11:41, Amir Michail via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
Sent from my iPad
On Jan 7, 2016, at 2:34 PM, Félix Cloutier <felixcca@yahoo.ca <mailto:felixcca@yahoo.ca>> wrote:
Yes, but following your suggestion, there may not be a difference between a non-optional value and an implicitly-wrapped optional, meaning that there will be a lot more of them.
Variables that are never assigned "none" need not have these runtime checks. Alternatively, you can have a type suffix similar to ? to indicate that a variable may be in an uninitialized state.
Félix
Le 7 janv. 2016 à 14:10:44, Amir Michail <a.michail@me.com <mailto:a.michail@me.com>> a écrit :
On Jan 7, 2016, at 2:09 PM, Félix Cloutier <felixcca@yahoo.ca <mailto:felixcca@yahoo.ca>> wrote:
That would leave you with runtime checks instead of compile-time checks and I totally disagree with that.
Implicitly unwrapped optionals do runtime checks also.
Félix
Le 7 janv. 2016 à 13:45:21, Amir Michail <a.michail@me.com <mailto:a.michail@me.com>> a écrit :
On Jan 7, 2016, at 1:40 PM, Félix Cloutier <felixcca@yahoo.ca <mailto:felixcca@yahoo.ca>> wrote:
An implicitly-unwrapped optional would do almost that, no?
You can use “none” to eliminate implicitly unwrapped optionals from the language.
Félix
Le 7 janv. 2016 à 12:46:53, Amir Michail via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> a écrit :
Examples:
var x:Int = none // uninitialized but not an optional
print(x) // run-time error as x is uninitialized
if x == nil { … } // compile time error… x can never be nil because it is not an optional
if x == none { x = 2 } // … but it can be uninitialized
Optionals can also be uninitialized:
var y:Int? = none // uninitialized and an optional
if y == nil { … } // run-time error as y is uninitialized
y = nil
if y == nil { … } // fine
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