Info: https://github.com/Kametrixom/The-Swift-Make-It-Compile-Challenge

Challenge1.swift

// Make this code compile without changing these lines 

func raw<T: RawRepresentable>(t: T) -> T.RawValue {
	return t.rawValue
}

let array : [E] = [.A(true), .B(1), .C("C")]

array.map(raw)

if case .C(let s?)? = array.first {}

// If you want a bigger challenge, include this part:

for elem in array {
	switch elem {
	case .C(_):
		print("C!")
	}
}

enum E : RawRepresentable {
    case C(String?)

    init?(rawValue: String) {
        self = .C(rawValue)
    }

    static func A(x: Bool) -> E {
        return .C(String(x))
    }

    static func B(x: Int) -> E {
        return .C(String(x))
    }

    var rawValue: String {
        switch self {
        case let .C(value): return value ?? ""
        }
    }
}

Congrats to @kostiakoval for solving the challenge when there wasn't an extended version yet
Congrats to @pyrtsa for solving the extended challenge ;)