How can I use self for init in extension in Swift?

I want use self for having default value, but Xcode cannot find it! how can I solve the issue? I want to have a default value also an option to chose the range in case.

extension Array {
    func printItemsIn(range: Range<Int> = self.indices) {
        range.forEach { index in
            print(self[index])
        }
    }
}

use case:

[10, 20, 30, 40].printItemsIn(range: 0..<1)

>Solution :

You can’t. What you can do is declare your parameter as optional and set its default value to nil.

extension Array {
    func printItems(in range: Range<Int>? = nil) {
        let range = range ?? indices
        range.forEach { index in
            print(self[index])
        }
    }
}

[10, 20, 30, 40].printItems(in: 0..<1)  // 10
[10, 20, 30, 40].printItems()           // 10, 20, 30, 40