[swift-evolution] Proposal: partial initialization before returning nil from an initializer

Félix Cloutier felixcca at yahoo.ca
Thu Dec 17 10:23:04 CST 2015

Oh, sweet.

Is there a changelog anywhere? I really like LLVM's release notes and how they're updated during development.


> Le 17 déc. 2015 à 11:20:08, Keith Smiley <keithbsmiley at gmail.com> a écrit :
> I believe this has already been fixed here: https://github.com/apple/swift/commit/f524802e129f17de16fa6f8c3f08e5bcf75cc581 <https://github.com/apple/swift/commit/f524802e129f17de16fa6f8c3f08e5bcf75cc581>
> On Thu, Dec 17, 2015 at 10:01 Félix Cloutier <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Hi all,
> Initializers can now fail, but objects still need to be fully initialized before you can return `nil` from them. For instance:
>         class Foo {
>                 let bar: Int
>                 init?(baz: Int) {
>                         guard baz < 100 else {
>                                 return nil
>                         }
>                         self.bar = baz
>                 }
>         }
> This trivial example causes the following error: "all stored properties of a class instance must be initialized before returning nil from an initializer".
> For integers, that's easy: you can simply set them to zero. However, sometimes, you'd want initialization to fail because the arguments you received don't allow you to properly initialize a member. In these cases, you have to make the fields Optionals (implicitly unwrapped or not) to overcome this.
> I remember that Chris said that this is a temporary issue and that it would eventually be fixed. I'm starting this thread because I'd love to have this with or before Swift 3 and I'd like to see who thinks this is big enough of an issue to rival the proposals we already have.
> Félix
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