I started the migration of a project with the recommended wizard on Xcode 9 over a project that has both Objc and Swift working together.

The problem occurs when having the following `UIColor` extension:

```
extension UIColor {
    func doSomething(withAnotherColor color: UIColor) -> Bool {
        return true
    }
}

```

then on some Objc class:

```
@implementation MyView

    - (void)styleView {
        //... some code
        if ([someColor doSomethingWithAnotherColor:anotherColor]) {
            ... 
        }
    }
@end

```

The `if` statement is throwing the following error: `../MyView.m: No visible @interface for 'UIColor' declares the selector 'doSomethingWithAnotherColor:'`

I tried using `@objc` directive both on the extension and method without luck.

Note this is a **compilation error**, not a warning like mentioned on other questions, like this one: [How can I deal with @objc inference deprecation with #selector() in Swift 4?](https://stackoverflow.com/questions/44390378/how-can-i-deal-with-objc-inference-deprecation-with-selector-in-swift-4)

Any ideas?