Author: Lets Build That App
Video URL: Advanced Swift Tricks: Custom Array Extensions

import UIKit

extension Array where Element: Numeric {
    func customSum() -> Element {
        //return self.reduce(0, {$0 + $1})
        return self.reduce(0, +)
    }
}

[2.3, 3, 4.7].customSum()

extension Array where Element == String {
    func concatenate() -> String {
        return self.reduce("", {$0 + $1 + " "})
    }
}

["Hello", "From", "wangmingjun.com"].concatenate()