Safety Array subscript, And Safety Array for Optional Index

Array+Extension.swift

import Foundation

extension Array {
    public subscript (safe index: Array.Index) -> Element? {
        get {
            return indices ~= index ? self[index] : nil
        }
        set {
            guard let element = newValue else { return }
            self[index] = element
        }
    }
}

extension Array {
    subscript (safe index: Array.Index?) -> Element? {
        get {
            guard let index = index else { return nil }
            return indices ~= index ? self[index] : nil
        }
        set {
            guard let index = index else { return }
            guard let element = newValue else { return }
            if indices ~= index
                self[index] = element
        }
    }
}