字符串slice是String的一部分引用
字面值就是slice
其他类型的slice

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fn main()

{
  let s = String::from("Hello World");

  let h = &s[0..5];//从0到5之前
                   //let h = &s[0..=4];
                   //let h = &s[..=4];
                   //let h = &s[..5]
  let w = &s[6..11];
  let w = &s[6..=10];
  let w = &s[..];//等于整个s
  println!("w= {}",w);

  let ss = String::from("你好");
  let w1 = &s[0..1];//报错，这个是因为char为32位。
  println!("h = {}",h);

  let s3 = "hh";//slice(或者叫做&str)，相当于不可变引用
  let a = [1,2,3,4];
  let sss = &a[1..3];
  println!("sss = {}",sss[0]);
  println!("sss = {}",sss[1]);
}