字符
正式介绍字符串之前呢，需要引入一个新的数据类型，即字符（Character），字符类型只能存放一个字符，例如：
var ch : Character = "!"
单独的一个字符可以拼接在一个字符串的后面，具体方法如下：
var str = "Hello, playground"
str.append(ch)
字符串
//常量字符串，不能对其进行重新赋值或者拼接等操作
let str2 = "I'm an immutable string"
//可变字符串
var str = "你好, playground"
//字符串的拼接
str += "\u{1F496}"
//初始化一个空的字符串
//方法一
var emptyString = ""
//方法二 实际上是创建了一个字符串类的对象
var anotherEmptyString = String()
//判断当前字符串是否为空,返回的是一个Bool类型
str.isEmpty
//字符串的遍历
for c in str.characters
{
print(c)
}
//计算字符串的长度
str.characters.count
//字符串的插值 String Interpolation
let imInt:Int = 2
let imTouble:(Bool,Float) = (true,1.1435926)
print("\(imInt),\(imTouble.0)")
//输出结果为：2,true
//字符串的比较
let str_a = "abc"
let str_b = "abc"
str_a == str_b //true
let str_c = "abd"
str_a < str_c //true
let str_d = "abcd"
str_c < str_d //false
//前缀和后缀的判断
str.hasPrefix("http") //false
str.hasSuffix("playground") //true
//import Foundation以后就可以用String来使用OC中NSString中的所有方法
import Foundation
// 下面的大小写转换的方法均不改变str本身的值
//把字符串中的每一个单词的首字母都转换成大写
str.capitalized
//把字符串中所有的字符转换成大写
str.uppercased()
//把字符串
str.lowercased()
//trim操作，即对字符串头尾中没有用的字符进行截取，只保留中间有用的部分
var str3 = " !so cool "
str3.trimmingCharacters(in: NSCharacterSet.whitespaces) //!so cool
str3.trimmingCharacters(in: NSCharacterSet.init(charactersIn: " !") as CharacterSet)//so cool
//字符串的分割：把字符串按某个字符或字符串截取成一个一个的单词
var str4 = "welcom to play"
str4.components(separatedBy: " ") //["welcom", "to", "play"]
str4 = "welcoom to play swift!Step-by-step learn from now"
str4.components(separatedBy: NSCharacterSet.init(charactersIn: " !-") as CharacterSet)//["welcoom", "to", "play", "swift", "Step", "by", "step", "learn", "from", "now"]
//join 字符串的连接
var arry = ["a","b","c"]
let res = arry.joined(separator: "_") //"a_b_c"
//查找字符串中某个字符穿出现的范围
str4.range(of:"play")
str4.range(of: "welcom", options: String.CompareOptions.caseInsensitive)//忽略大小写进行查找
str4.startIndex
str4.endIndex
//截取字符串
let startIndex:String.Index = str4.startIndex
let endIndex:String.Index = str4.index(str4.startIndex, offsetBy: 8)
//下面的写法在swift 3.0中是错误的
//let strRange = Range<String.Index>(start:startIndex,end:endIndex)
//swift 3.0中的正确写法为
let strRange = startIndex ..< endIndex
str4.substring(with: strRange) //"welcome t"
str4.substring(to: endIndex) //"welcome t"
str4.substring(from: startIndex)
//插入字符串
var insertIndex = str4.index(str4.startIndex, offsetBy: 2)
str4.insert("!", at: insertIndex)
//删除字符
str4.remove(at: insertIndex)
str4.removeSubrange(strRange)
//替换字符串
str4.replaceSubrange(strRange, with: "hello")
关于字符串的更多操作后续补充，可参考这里
