[swift-evolution] Pitch: Remove default initialization of optional bindings

[Slava Pestov]

> On Nov 7, 2017, at 11:22 PM, Howard Lovatt via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Not a big deal either way, but I prefer the 2nd (nil) form and therefore would like to see the 1st form go. It would make Swift more consistent, consider:
> 
> let o: Int? // Looks like nil is assigned.
> if someTest {
>     o = 1 // Why isn't this an error? (OK I know why - but it looks odd.)
> } else {
>     o = nil
> }
> 
> 
> Whilst the above works it is weird because if you are aware that o: Int? normally assigns nil then the above looks like o, which is a let, is assigned to twice. If you do the equivalent of the above for a non-optional it is an error.

The default initialization behavior is specifically not enabled for let bindings. Compare:

let x: Int?
print(x as Any) // error: constant 'x' used before being initialized

var y: Int?
print(y as Any)

So your example is perfectly consistent, because you’re only initializing ‘o’ once (along each control flow path).

Slava

> 
>   -- Howard.
> 
> On 8 November 2017 at 07:54, Adrian Zubarev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Same here, but I wouldn’t care much if it were gone.
> 
> 
> Am 7. November 2017 um 21:40:56, David Hart via swift-evolution (swift-evolution at swift.org <mailto:swift-evolution at swift.org>) schrieb:
> 
>> Yeah, I use the first form constantly.
>> 
>> > On 6 Nov 2017, at 23:33, Slava Pestov via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> > 
>> > Hi all,
>> > 
>> > Right now, the following two declarations are equivalent:
>> > 
>> > struct S {
>> > var x: Int?
>> > }
>> > 
>> > struct S {
>> > var x: Int? = nil
>> > }
>> > 
>> > That is, mutable bindings of sugared optional type (but not Optional<T>!) always have a default value of ‘nil’. This feature increases the surface area of the language for no good reason, and I would like to deprecate it in -swift-version 5 with a short proposal. Does anyone feel strongly about giving it up? I suspect most Swift users don’t even know it exists.
>> > 
>> > Slava
>> > _______________________________________________
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>> 
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