This extension to Array provides safe access to any index in an array, with a clean non-crashy result.

Array+SafeIndexAccessible.swift

//
//  Array_SafeAccess.swift
//
//  Created by Zhao, Tyler on 6/26/19.
//

import Foundation

/// This protocol describes a function designed to return an optional
/// on a bad array access.
public protocol SafeIndexAccessible {
    // swiftlint:disable missing_docs
    associatedtype Element
    // swiftlint:enable missing_docs

    /// Safe access to objects in an array. On a bad access, nil is returned.
    /// Usage:
    /// ```
    /// let myArr = [Double](repeating: 2.0, count 3) // Creates an array of size 3.
    /// let test = myArr[safe: 3] // test is nil, as there is no array element at index 3.
    /// ```
    subscript(safe index: Int) -> Element? { get }
}

extension Array: SafeIndexAccessible {
    public subscript(safe index: Int) -> Element? {
        guard indices.contains(index) else { return nil }
        return self[index]
    }
}