Add ++ & -- operators to Int in Swift 4

Utils.swift

infix operator ++
infix operator --

extension Int {
    
    /// decress the value by one
    ///
    /// - Parameter num: value to decress
    static prefix func --(_ num: inout Int) -> Int {
        num -= 1
        return num
    }
    
    /// decress the value by one
    ///
    /// - Parameter num: value to decress
    static postfix func --(_ num: inout Int) -> Int {
        let oldValue = num
        num -= 1
        return oldValue
    }
    
    /// increase the value by one
    ///
    /// - Parameter num: value to increase
    static prefix func ++(_ num: inout Int) -> Int {
        num += 1
        return num
    }
    
    /// increase the value by one
    ///
    /// - Parameter num: value to increase
    static postfix func ++(_ num: inout Int) -> Int {
        let oldValue = num
        num += 1
        return oldValue
    }
}