String extension to get a substring by UInt indexes.

StringExtensionSubstring.swift

extension String {
    func substring(from: UInt, length: UInt) -> String {
        if Int(from) >= self.characters.count {
            preconditionFailure("from is out of bounds.")
        }
        if Int(from+length) > self.characters.count {
            preconditionFailure("from and lenght are out of bounds")
        }
        
        let startIndex = self.index(self.startIndex, offsetBy: String.IndexDistance(from))
        let endIndex = self.index(self.startIndex, offsetBy: String.IndexDistance(from+length))
        
        return self.substring(with: startIndex..<endIndex)
    }
    func substring(from: UInt) -> String {
        if Int(from) >= self.characters.count {
            preconditionFailure("from is out of bounds.")
        }
        
        let startIndex = self.index(self.startIndex, offsetBy: String.IndexDistance(from))
        
        return self.substring(from: startIndex)
    }
}