//原始字符串
let str1 = " jack "
//除去前后空格
let str2 = str1.trimmingCharacters(in: .whitespaces)
CharacterSet 里各個(gè)枚舉類型的含義如下：
controlCharacters：控制符
whitespaces：空格
newlines：換行符
whitespacesAndNewlines：空格換行
decimalDigits：小數(shù)
etters：文字
lowercaseLetters：小寫字母
uppercaseLetters：大寫字母
nonBaseCharacters：非基礎(chǔ)
alphanumerics：字母數(shù)字
decomposables：可分解
illegalCharacters：非法
punctuationCharacters：標(biāo)點(diǎn)
capitalizedLetters：大寫
symbols：符號(hào)
刪除前后指定的字符
//原始字符串
let str1 = "--天啊--"
//刪除前后<>
let characterSet = CharacterSet(charactersIn: "--")
let str2 = str1.trimmingCharacters(in: characterSet)
substring swift3.0和swift4.0區(qū)別
let newStr = String(str[..<index]) // = str.substring(to: index) In Swift 3
let newStr = String(str[index...]) // = str.substring(from: index) In Swif 3
let newStr = String(str[range]) // = str.substring(with: range) In Swift 3
