This is an easy way to apply operation to generic numbers (Int, Float, Double, etc.)

Swift generic numbers operations.swift

protocol Math {
    static func +(lhs: Self, rhs: Self) -> Self
    static func *(lhs: Self, rhs: Self) -> Self
    init()
}

//Extend all numbers you want to
extension Int : Math {}
extension Double : Math {}
extension Float : Math {}

extension Collection where Iterator.Element == Math {
    
    func sum<T : Math>(_ x:T...) -> T {
        
        return self.flatMap { $0 as? T }.reduce(x.reduce(T()) { $0 + $1}) { $0 + $1 }
    }
    
    func product<T : Math>(_ x:T...) -> T {
    
        return self.flatMap { $0 as? T }.reduce(x.reduce(T()) { $0 * $1}) { $0 * $1 }
    }
}

let a = [1,2,3].sum(10, 20, 30) //66
let b = [1.1,2.1,3.1].sum(1.0) //7.3
let c = [2,3].product(4)//24
let d = [1.3, 2.4].product(3.3, 4.5)//46.332