Conformance in an extension

The second way to declare a conformance is to add the conformance to an extension. The main benefit is that you can add functionalities, in the form of extensions, to existing types. The other main benefit of declaring a conformance inside of an extension is that you can scope this conformance to a particular file or module, with the private modifier.

For example, suppose that we want to add the toggle method to the Bool type, but only for the current file or your framework. You may not want it to leak outside, as the implementation may conflict with another one:

internal extension Bool: Toggling {
    mutating func toggle() {
        self = !self
    }
}

var isReady = false
isReady.toggle()
assert(isReady)