在Rust中，“让x = ~10;”过时了吗？

Question

I read this tutorial and tried the following Rust code:

fn main() {
    let x = ~10;
    println!("{:d}", *x);
}

But the compiler complains:

rustc 1.16.0 (30cf806ef 2017-03-10)
error: expected expression, found `~`
 --> <anon>:2:13
  |
2 |     let x = ~10;
  |             ^

error: unknown format trait `d`
 --> <anon>:3:22
  |
3 |     println!("{:d}", *x);
  |                      ^^

Is let x = ~10; obsolete already?

Answer 1

It is very obsolete. Rust 1.0 was released on 2015-05-15. This syntax was removed months before that. That means that your tutorial hasn't been updated in a long time; in fact, that file was last updated on 2014-01-28! Not a good sign.

The non-obsolete version of your code:

fn main() {
    let x = Box::new(10);
    println!("{}", x);
}

1. The sigil ~ was replaced with specific data structures. In this case, Box .
2. The format specifier :d no longer exists. Just use the Display formatter {} .
3. There's no need to dereference the boxed number.

---

Instead of some "already obsolete" reference, use the official sources:

• The Rust Programming Language , Second Edition
• The Rust Programming Language , First Edition
• Rust by Example