The Swift Make-It-Compile Challenge #4
I'm posting this answer on behalf of Chris Goldsby who managed to submit a
99% Solution (Gist):
typealias D = NonObjectiveCBase

func ~=(left: Any, right: Bool) -&gt; BooleanType {
    return true
}

func +(left: Any, right: Any) -&gt; String {
    return &quot;&quot;
}

protocol &amp;#128034;: class, BooleanType, ArrayLiteralConvertible {
    
    var `self` : () -&gt; () { get set }
}

extension &amp;#128034; {
    
    typealias Element = Any
    
    internal init(arrayLiteral elements: Any...) {
        self.init()
    }
    
    //
    
    func doIt(inout s: D) {
        if case self = isUniquelyReferenced(&amp;s),
            self.`self` = true where self {
            self.`self` = { [unowned x = [self, 7] as Self] n in
                print(x + n)
            } as () -&gt; ()
        }
    }
    
    //
    
}

Only the snytax highlighting of D doesn't match. That's remarkable as it is!
100% Solution
EDIT: Two days later he submitted the following full solution, congrats!:
private func ~=(left: Any, right: Bool) -&gt; BooleanType {
    return true
}

private func +(left: Any, right: Any) -&gt; String {
    return &quot;&quot;
}

protocol Challenge4: class, BooleanType, ArrayLiteralConvertible {
    
    typealias D
    
    var `self` : () -&gt; () { get set }
    
    func doIt(inout s: D)
}

private extension Challenge4 where D == NonObjectiveCBase {
    
    typealias Element = Any
    
    init(arrayLiteral elements: Any...) {
        self.init()
    }
    
    //
    
    func doIt(inout s: D) {
        if case self = isUniquelyReferenced(&amp;s),
            self.`self` = true where self {
            self.`self` = { [unowned x = [self, 7] as Self] n in
                print(x + n)
            } as () -&gt; ()
        }
    }
    
    //
    
}