[swift-evolution] Proposal: label-only constructors

[Drew Crawford]

The problems with enums as parameters were explained in the proposal.  I don't see how these responses address any of the concerns that were initially raised.


> On Dec 13, 2015, at 2:25 PM, David Owens II via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Agreed. It's also likely that you'll be setting some internal flag with this information already. 
> 
> Sent from my iPhone
> 
> On Dec 13, 2015, at 8:55 AM, Harlan Haskins via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> Also I think it’d be cleaner to just accept an enum in one initializer
>> 
>> enum KeyType {
>>     case RSA
>>     case Curve25519
>>     case AES
>> }
>> 
>> Then you get that semantic niceness of:
>> 
>> init(keyType: .RSA)
>> init(keyType: .Curve25519)
>> init(keyType: .AES)
>> 
>> — Harlan
>> 
>>> On Dec 13, 2015, at 11:41 AM, Sean Heber via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> In this particular example, perhaps Key should be an enum instead of a struct.
>>> 
>>> l8r
>>> Sean
>>> 
>>> Sent from my iPad
>>> 
>>> On Dec 13, 2015, at 10:07 AM, ilya via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>>> Good point on that. I still think the best solution is to take the existing syntax of
>>>> 
>>>> 
>>>> struct Key {
>>>>     init(forRSA:Void) { /* */ }
>>>>     init(forCurve25519:Void) { /* */ }
>>>>     init(forAES:Void) { /* */ }
>>>> }
>>>> 
>>>> let a = Key(forRSA: ())
>>>> 
>>>> or 
>>>> 
>>>> let empty: Void = ()
>>>> let c = Key(forAES: empty)
>>>> 
>>>> and make it somewhat easier to read.  Perhaps
>>>> 
>>>> let b = Key(forCurve25519: _ )
>>>> 
>>>> I think many people will read Key(forAES) as Key.init(_: forAES), so that may be not the best expression here.
>>>> 
>>>> 
>>>> 
>>>> On Sun, Dec 13, 2015 at 4:21 PM, Drew Crawford <drew at sealedabstract.com <mailto:drew at sealedabstract.com>> wrote:
>>>> 
>>>>> On Dec 13, 2015, at 7:13 AM, ilya <ilya.nikokoshev at gmail.com <mailto:ilya.nikokoshev at gmail.com>> wrote:
>>>>> 
>>>>> You can easily call a private parametrized init from a class function though. 
>>>> 
>>>> 
>>>> Sure, but we're just shuffling the deck.  We've gone from a bad public API to a bad private API.
>>>> 
>>>> Actually, it's worse, because we now have BOTH a bad private API AND a bad public API.  There is a reason that NSData.dataWithData(...) is a Swift compile error.
>>>> 
>>>> The (ab)use of class functions as constructors is a holdover from ObjC times.  If you want to make an instance in Swift, you should type ClassName( and see what autocomplete suggests; you should not have to read through the documentation of class functions to see if they are secretly constructors that have been filed at the wrong shelf in the library.
>>>> 
>>>> 
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