Swift string random access extension (fuckin' slow)

stringExtension.swift

// Too bad extension. Bad I think it is the best way.
extension String {
    subscript(index: Int) -> Character {
        return self[self.index(self.startIndex, offsetBy: index)]
    }

    subscript(bounds: CountableRange<Int>) -> Substring {
        return self[index(at: bounds.lowerBound)..<index(at: bounds.upperBound)]
    }

    subscript(bounds: CountableClosedRange<Int>) -> Substring {
        return self[index(at: bounds.lowerBound)...index(at: bounds.upperBound)]
    }

    subscript(bounds: PartialRangeUpTo<Int>) -> Substring {
        return self[..<index(at: bounds.upperBound)]
    }

    subscript(bounds: PartialRangeThrough<Int>) -> Substring {
        return self[...index(at: bounds.upperBound)]
    }

    subscript(bounds: PartialRangeFrom<Int>) -> Substring {
        return self[index(at: bounds.lowerBound)...]
    }

    subscript(bounds: CountableRange<Int>) -> String {
        return String(self[index(at: bounds.lowerBound)..<index(at: bounds.upperBound)])
    }

    subscript(bounds: CountableClosedRange<Int>) -> String {
        return String(self[index(at: bounds.lowerBound)...index(at: bounds.upperBound)])
    }

    subscript(bounds: PartialRangeUpTo<Int>) -> String {
        return String(self[..<index(at: bounds.upperBound)])
    }

    subscript(bounds: PartialRangeThrough<Int>) -> String {
        return String(self[...index(at: bounds.upperBound)])
    }

    subscript(bounds: PartialRangeFrom<Int>) -> String {
        return String(self[index(at: bounds.lowerBound)...])
    }

    func index(at offset: Int) -> String.Index {
        return index(startIndex, offsetBy: offset)
    }
}