iOS Xcode Swift autocomplete broken?

Question

I haven't used Swift that much but coming from Objective C, there's a few things about Swift that's a PITA to get my head around. In iOS programming, we have `animateWithDuration:` method, which is part of UIView. So I tried to use Xcode's autocomplete and begin to type: ``` UIView.animateWith ``` The autocomplete shows: ``` UIView.animateWithDuration(duration: NSTimeInterval, animations: () -> Void) ``` I then tabbed across to the "duration" field, and then typed in a number: ``` UIView.animateWithDuration(0.5, animations: () -> Void) ``` Then I tabbed across again to the animation block, and pressed enter like how I normally do it in Objective C, Xcode now shows: ``` UIView.animateWithDuration(0.5, animations: { () -> Void in code }) ``` So then I tabbed one last time to replace "code" with my code: ``` UIView.animateWithDuration(0.5, animations: { () -> Void in self.customView?.transform = CGAffineTransformMakeTranslation(0.0, 0.0); }) ``` That's when Xcode then gives me the error:…

Accepted Answer

From "Calling Methods Through Optional Chaining":

Any attempt to set a property through optional chaining returns a value of type `Void?`, which enables you to compare against nil to see if the property was set successfully ...

Therefore the type of the expression

```
self.customView?.transform = CGAffineTransformMakeTranslation(0.0, 0.0)
```

is `Void?` (optional Void). And if a closure consists only of a single expression, then this expression is automatically taken as the return value. The error message is quite misleading, but it comes from the fact that `Void?` is different from `Void`.

Adding an explicit `return` statement solves the problem:

```
UIView.animateWithDuration(0.5, animations: { () -> Void in
    self.customView?.transform = CGAffineTransformMakeTranslation(0.0, 0.0)
    return
})
```

Update: Adding an explicit `return` statement it not necessary anymore with Swift 1.2 (Xcode 6.3). From the beta release notes:

Unannotated single-expression closures with non-Void return types can now be used in Void contexts.

iOS Xcode Swift autocomplete broken?

Solution

Problem