gistfile1.swift

protocol Arithmeticable {
    init(_ v: Int)
    func +(lhs: Self, rhs: Self) -> Self
    func -(lhs: Self, rhs: Self) -> Self
    func *(lhs: Self, rhs: Self) -> Self
    func /(lhs: Self, rhs: Self) -> Self
}

extension Int: Arithmeticable {}
extension Double: Arithmeticable {}

func sqrt<T: Arithmeticable>(x: T) -> T {
    var guess = x;
    for i in 0..100 {
        guess = (guess + x / guess) / T(2)
    }
    return guess
}

func quadratic<T: Arithmeticable>(a: T, b: T, c: T) -> (T, T) {
    return (
        (T(0)-b + sqrt(b * b - T(4) * a * c)) / (T(2) * a),
        (T(0)-b - sqrt(b * b - T(4) * a * c)) / (T(2) * a)
    )
}

println(quadratic(1, 0, -1))
println(quadratic(2.0, 0.0, -1.0))