如何在Rust中打印变量并让它显示有关该变量的所有内容，例如Ruby的.inspect？

Question

use std::collections::HashMap;

fn main() {
    let mut hash = HashMap::new();
    hash.insert("Daniel", "798-1364");
    println!("{}", hash);
}

将无法编译：

error[E0277]: `std::collections::HashMap<&str, &str>` doesn't implement `std::fmt::Display`
 --> src/main.rs:6:20
  |
6 |     println!("{}", hash);
  |                    ^^^^ `std::collections::HashMap<&str, &str>` cannot be formatted with the default formatter
  |

有没有办法说出类似的话：

println!("{}", hash.inspect());

打印出来：

1) "Daniel" => "798-1364"

Answer 1

您正在寻找的是Debug格式化程序：

use std::collections::HashMap;

fn main() {
    let mut hash = HashMap::new();
    hash.insert("Daniel", "798-1364");
    println!("{:?}", hash);
}

这应该打印：

{"Daniel": "798-1364"}

另见：

• What is the difference between println's format styles?

Answer 2

Rust 1.32引入了dbg宏：

use std::collections::HashMap;

fn main() {
    let mut hash = HashMap::new();
    hash.insert("Daniel", "798-1364");
    dbg!(hash);
}

这将打印：

[src/main.rs:6] hash = {
    "Daniel": "798-1364"
}