[String Extensions] #string #subscript #encoding

String+Extensions.swift

import Foundation

extension CFStringEncodings {
    var encoding: String.Encoding {
        return String.Encoding(rawValue: CFStringConvertEncodingToNSStringEncoding(CFStringEncoding(self.rawValue)))
    }
}

public extension String.Encoding {
    public static let big5 = CFStringEncodings.big5.encoding
    public static let gb18030 = CFStringEncodings.GB_18030_2000.encoding
}

public extension String {
    subscript(position: Int) -> Character? {
        guard let pos = index(startIndex, offsetBy: position, limitedBy: endIndex) else { return nil }
        return self[pos]
    }

    subscript(range: Range<Int>) -> String? {
        guard let start = index(startIndex, offsetBy: range.lowerBound, limitedBy: endIndex) else { return nil }
        guard let end = index(startIndex, offsetBy: range.upperBound, limitedBy: endIndex) else { return nil }
        return String(self[start..<end])
    }

    subscript(range: ClosedRange<Int>) -> String? {
        guard let start = index(startIndex, offsetBy: range.lowerBound, limitedBy: endIndex) else { return nil }
        guard let end = index(startIndex, offsetBy: range.upperBound, limitedBy: endIndex) else { return nil }
        return String(self[start...end])
    }

    subscript(range: PartialRangeFrom<Int>) -> String? {
        guard let start = index(startIndex, offsetBy: range.lowerBound, limitedBy: endIndex) else { return nil }
        return String(self[start...])
    }

    subscript(range: PartialRangeUpTo<Int>) -> String? {
        guard let end = index(startIndex, offsetBy: range.upperBound, limitedBy: endIndex) else { return nil }
        return String(self[..<end])
    }

    subscript(range: PartialRangeThrough<Int>) -> String? {
        guard let end = index(startIndex, offsetBy: range.upperBound, limitedBy: endIndex) else { return nil }
        return String(self[...end])
    }
}