Subscript `String` safely with `Optional`

String+SafeSubscript.swift

import Foundation

extension String {
    subscript(safe range: String.IndexDistance) -> Character? {
        guard let index = index(at: range) else { return nil }

        return self[index]
    }

    subscript(safe range: NSRange) -> Substring? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return self[lowerBound..<upperBound]
    }

    subscript(safe range: NSRange) -> String? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return String(self[lowerBound..<upperBound])
    }

    subscript(safe range: Range<String.IndexDistance>) -> Substring? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return self[lowerBound..<upperBound]
    }

    subscript(safe range: Range<String.IndexDistance>) -> String? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return String(self[lowerBound..<upperBound])
    }

    subscript(safe range: ClosedRange<String.IndexDistance>) -> Substring? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return self[lowerBound...upperBound]
    }

    subscript(safe range: ClosedRange<String.IndexDistance>) -> String? {
        guard let lowerBound = index(at: range.lowerBound),
              let upperBound = index(at: range.upperBound)
        else { return nil }

        return String(self[lowerBound...upperBound])
    }

    subscript(safe range: PartialRangeUpTo<String.IndexDistance>) -> Substring? {
        guard let upperBound = index(at: range.upperBound) else { return nil }

        return self[..<upperBound]
    }

    subscript(safe range: PartialRangeUpTo<String.IndexDistance>) -> String? {
        guard let upperBound = index(at: range.upperBound) else { return nil }

        return String(self[..<upperBound])
    }

    subscript(safe range: PartialRangeThrough<String.IndexDistance>) -> Substring? {
        guard let upperBound = index(at: range.upperBound) else { return nil }

        return self[...upperBound]
    }

    subscript(safe range: PartialRangeThrough<String.IndexDistance>) -> String? {
        guard let upperBound = index(at: range.upperBound) else { return nil }

        return String(self[...upperBound])
    }

    subscript(safe range: PartialRangeFrom<String.IndexDistance>) -> Substring? {
        guard let lowerBound = index(at: range.lowerBound) else { return nil }

        return self[lowerBound...]
    }

    subscript(safe range: PartialRangeFrom<String.IndexDistance>) -> String? {
        guard let lowerBound = index(at: range.lowerBound) else { return nil }

        return String(self[lowerBound...])
    }
}

private extension String {
    func index(at offset: String.IndexDistance) -> String.Index? {
        index(startIndex, offsetBy: offset, limitedBy: endIndex)
    }
}