类型“字符串”不符合协议“序列”

Question

当我尝试打印字符串a中的每个字符时，为什么会出现这种情况？

import Foundation


let a = "what is this"
for b in a {
    print(b)
}

Answer 1

String不是序列，您需要调用characters属性以获取sequence 。

let a = "what is this"
for b in a.characters {
  print(b, terminator: "")
}

// "what is this"

Answer 2

如果要枚举所有字符，则必须使用String的characters成员变量。

let a = "what is this"
for b in a.characters 
{
   print(b)
}