[swift-evolution] IUO in Swift 3.0

[Joe Groff]

> On Jun 21, 2016, at 1:06 PM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Just saw this article about IUO in Swift 3.0:
> 
> https://www.bignerdranch.com/blog/wwdc-2016-increased-safety-in-swift-3/
> 
> I was surprised that the IUO type still exists. From what I understood, SE-0054 gives a clear example that:
> 
> func f() -> Int! { return 3 } 
> // f: () -> Int?, has IUO attribute
> // ...
> 
> let x3: Int! = f() 
> // succeeds; x3: Int? = .some(3), has IUO attribute
> // ...
> 
> func g() -> Int! { return nil } 
> // f: () -> Int?, has IUO attribute
> // ...
> 
> let y3: Int! = g() // succeeds; y3: Int? = .none, has IUO attribute
> 
> x3 and y3 should be a of type Int? but trying those out in Xcode 8’s beta 1 playground show that they are still of type Int!. Did I miss something?

SE-0054 hasn't been fully implemented yet. The stricter implicit promotions are mostly there, but the IUO type still exists.

-Joe