Swift 3 Trimming of special characters

Trim.swift

extension String {
	
	func trim(_ string: String) -> String {
		var set = Set<Character>()
		for c in string.characters {
			set.insert(Character(String(c)))
		}
		return trim(set)
	}
	
	func trim(_ characters: Set<Character>) -> String {
		if let index = self.characters.index(where: {!characters.contains($0)}) {
			return self[index..<self.endIndex]
		} else {
			return ""
		}
	}
	
}