元组和数组

元组和数组是我们见过的第一个 “复合”类型。数组的所有元素具有相同的类型，而元组可以适应不同的类型。这两种类型的大小在编译时是固定的。

	类型	字面量
数组（Arrays）	`[T; N]`	`[20, 30, 40]`, `[0; 3]`
元组（Tuples）	`()`, `(T,)`, `(T1, T2)`, ...	`()`, `('x',)`, `('x', 1.2)`, ...

数组的赋值和访问操作：

fn main() {
    let mut a: [i8; 10] = [42; 10];
    a[5] = 0;
    println!("a: {a:?}");
}

元组的赋值和访问操作：

fn main() {
    let t: (i8, bool) = (7, true);
    println!("t.0: {}", t.0);
    println!("t.1: {}", t.1);
}

关键点：

数组：

A value of the array type [T; N] holds N (a compile-time constant) elements of the same type T. Note that the length of the array is part of its type, which means that [u8; 3] and [u8; 4] are considered two different types. Slices, which have a size determined at runtime, are covered later.
请尝试访问出界数组元素。系统会在运行时检查数组访问。Rust 通常会通过优化消除这些检查，以及使用不安全的 Rust 来避免这些检查。
我们可以使用字面量来为数组赋值。
The println! macro asks for the debug implementation with the ? format parameter: {} gives the default output, {:?} gives the debug output. Types such as integers and strings implement the default output, but arrays only implement the debug output. This means that we must use debug output here.
添加 #，比如 {a:#?}，会输出“美观打印（pretty printing）” 格式，这种格式可能会更加易读。

元组：

和数组一样，元组也具有固定的长度。
元组将不同类型的值组成一个复合类型。
元组中的字段可以通过英文句号加上值的下标进行访问比如：t.0, t.1。
The empty tuple () is also known as the “unit type”. It is both a type, and the only valid value of that type --- that is to say both the type and its value are expressed as (). It is used to indicate, for example, that a function or expression has no return value, as we’ll see in a future slide.
- You can think of it as void that can be familiar to you from other programming languages.

Comprehensive Rust 🦀