Cannot call value of non-function type 'CIImage?'

Question

This code does compile perfectly fine

let ciImage = CIImage(image:UIImage())

however when I move it into an extension of UIImage

extension UIImage {
    func foo() {
        let ciImage = CIImage(image:UIImage()) // compile error
    }
}

I get the following compile error

Cannot call value of non-function type 'CIImage?'

Why?

---

Tested with Xcode Playground 7.1.1. and Swift 2.1

Answer 1

It's because, once inside UIImage, the term CIImage is seen as the CIImage property of UIImage, due to implicit self as message recipient — in other words, Swift turns your CIImage into self.CIImage and it's all downhill from there.

You can solve this by disambiguating thru Swift's use of module namespacing:

extension UIImage {
    func foo() {
        let ciImage = UIKit.CIImage(image:UIImage())
    }
}

EDIT In Swift 3 this problem will go away, because all properties will start with small letters. The property will be named ciImage, and there will be no confusion with the CIImage class.