Subscript `String` using the range expression

String+Subscript.swift

import Foundation

extension String {
    subscript(range: String.IndexDistance) -> Character {
        self[index(at: range)]
    }

    subscript(range: NSRange) -> Substring {
        self[range.lowerBound..<range.upperBound]
    }

    subscript(range: NSRange) -> String {
        String(self[range.lowerBound..<range.upperBound])
    }

    subscript(range: Range<String.IndexDistance>) -> Substring {
        self[index(at: range.lowerBound)..<index(at: range.upperBound)]
    }

    subscript(range: Range<String.IndexDistance>) -> String {
        String(self[index(at: range.lowerBound)..<index(at: range.upperBound)])
    }

    subscript(range: ClosedRange<String.IndexDistance>) -> Substring {
        self[index(at: range.lowerBound)...index(at: range.upperBound)]
    }

    subscript(range: ClosedRange<String.IndexDistance>) -> String {
        String(self[index(at: range.lowerBound)...index(at: range.upperBound)])
    }

    subscript(range: PartialRangeUpTo<String.IndexDistance>) -> Substring {
        self[..<index(at: range.upperBound)]
    }

    subscript(range: PartialRangeUpTo<String.IndexDistance>) -> String {
        String(self[..<index(at: range.upperBound)])
    }

    subscript(range: PartialRangeThrough<String.IndexDistance>) -> Substring {
        self[...index(at: range.upperBound)]
    }

    subscript(range: PartialRangeThrough<String.IndexDistance>) -> String {
        String(self[...index(at: range.upperBound)])
    }

    subscript(range: PartialRangeFrom<String.IndexDistance>) -> Substring {
        self[index(at: range.lowerBound)...]
    }

    subscript(range: PartialRangeFrom<String.IndexDistance>) -> String {
        String(self[index(at: range.lowerBound)...])
    }
}

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