[swift-evolution] [Draft] Abolish IUO type

James Campbell james at supmenow.com
Fri Mar 18 06:20:19 CDT 2016

One thing I've had bit me is the lack of some sort of confirmation, see
this example.

I have a objective-c method in a library like so:

- (void)observe:(CallbackBlock)block;

The CallbackBlock is a type def-ed block like so:

typedef void (^CallbackBlock)(FDataSnapshot *snapshot);

The parameter in the block gets converted into a IUO, I ended up releasing
an app that crashed due to that IUO being nil.

The code that crashed was something like this

object.observe {

There is no way to tell that the $0 was a IUO. The compiler didn't force me
to confirm in it in some way using a ! and unless I remembered to check the
header I would have a crash.

How would this work under your proposal ?


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On Fri, Mar 18, 2016 at 6:53 AM, Brent Royal-Gordon via swift-evolution <
swift-evolution at swift.org> wrote:

> > (Come to think of it, is there a cost to converting between `T?` and
> `T!`, or do they get optimized into the same thing?)
> I can't imagine there would be. @autounwrapped (or whatever) is a purely
> compile-time thing which tells the compiler to automatically insert a `!`
> operator if it will make the expression typecheck. Other than that
> compile-time behavior, `!` is an exact synonym for `?`.
> --
> Brent Royal-Gordon
> Architechies
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> swift-evolution mailing list
> swift-evolution at swift.org
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