I found out that {:?} prints an entire array in Rust. I want to know what is it called and how exactly it works. Is it only limited to printing arrays or could it also be used elsewhere for other purposes?

我发现{：？}在Rust中打印整个数组。我想知道它叫什么，它到底是怎么工作的。它是否仅限于打印阵列，或者也可以用于其他目的？

This is explained (along with the rest of the formatting syntax) in the std::fmt documentation.

在std：：fmt文档中解释了这一点(以及其余的格式化语法)。

{...} surrounds all formatting directives. : separates the name or ordinal of the thing being formatted (which in this case is omitted, and thus means "the next thing") from the formatting options. The ? is a formatting option that triggers the use of the std::fmt::Debug implementation of the thing being formatted, as opposed to the default Display trait, or one of the other traits (like UpperHex or Octal).

{...}包含所有格式化指令。：将要格式化的事物的名称或序号(在本例中省略，因此表示“下一事物”)与格式化选项分开。那个？是一个格式化选项，它触发正在格式化的对象的std：：fmt：：调试实现，而不是默认的显示特性或其他特性之一(如UpperHex或Octal)。

Thus, {:?} formats the "next" value passed to a formatting macro, and supports anything that implements Debug.

因此，{：？}格式化传递给格式化宏的“NEXT”值，并支持实现Debug的任何内容。

The Debug trait is one of the most commonly used in Rust.
It allows you to format the output in a programmer-facing, debugging context. The way you typically use it is like this:

Debug特性是Rust中最常用的特性之一。它允许您在面向程序员的调试上下文中格式化输出。通常使用它的方式如下所示：

let v = vec![1, 2, 3];
let s = format!("{:?}", v);

Also, as of Rust 1.58 you can Debug-format a variable by putting it right after the opening curly bracket, like this:

此外，从Rust 1.58开始，您可以通过将变量放在左花括号后面进行调试格式化，如下所示：

let s = format!("{v:?}");

If you want to Debug-format a custom type, such as a struct, you can simply use derive like this:

如果要调试格式化自定义类型(如结构)，只需使用如下所示的派生：

#[derive(Debug)]
struct Person {
    name: String,
    age: u8,
}