Fraction.swift

struct Fraction
{
    var numerator:   Int
    var denominator: Int
    
    init?(numerator: Int, denominator: Int)
    {
        if denominator == 0 { return nil }
        self.numerator = numerator
        self.denominator = denominator
    }
    
    static func +(lhs: Fraction, rhs: Fraction) -> Fraction
    {
        return lhs.add(fraction: rhs)
    }
    
    func add(fraction rightFraction: Fraction) -> Fraction
    {
        return Fraction(numerator: numerator * rightFraction.denominator + rightFraction.numerator * denominator, denominator: denominator * rightFraction.denominator)!
    }
    
    nonmutating func simplified() -> Fraction
    {
        let gcdOfNumeratorAndDenominator: Int = gcd(a: self.numerator, self.denominator)
        return Fraction(numerator: self.numerator / gcdOfNumeratorAndDenominator, denominator: self.denominator / gcdOfNumeratorAndDenominator)!
    }
    
    mutating func simplify()
    {
        let gcdOfNumeratorAndDenominator: Int = gcd(a: self.numerator, self.denominator)
        self.numerator /= gcdOfNumeratorAndDenominator
        self.denominator /= gcdOfNumeratorAndDenominator
    }
    
    private func gcd(a: Int, _ b: Int) -> Int
    {
        var (a, b) = (a, b)
        while b != 0
        {
            (a, b) = (b, a % b)
        }
        return a
    }
}

extension Fraction: CustomStringConvertible
{
    var description: String { return "\(numerator)/\(denominator)" }
}