String Indexation in Swift

String+Indexation.swift

extension StringProtocol {
    subscript(_ offset: Int) -> Element { 
        return self[index(startIndex, offsetBy: offset)]
    }
    
    subscript(_ range: Range<Int>) -> SubSequence {
        return prefix(range.lowerBound+range.count).suffix(range.count)
    }
    
    subscript(_ range: ClosedRange<Int>) -> SubSequence {
        return prefix(range.lowerBound+range.count).suffix(range.count) 
    }
    
    subscript(_ range: PartialRangeThrough<Int>) -> SubSequence {
        return prefix(range.upperBound.advanced(by: 1)) 
    }
    
    subscript(_ range: PartialRangeUpTo<Int>) -> SubSequence {
        return prefix(range.upperBound) 
    }
    
    subscript(_ range: PartialRangeFrom<Int>) -> SubSequence {
        return suffix(Swift.max(0, count-range.lowerBound)) 
    }
}