元组

元组是不同类型值的集合。元组使用圆括号 () 构造，每个元组本身就是一个类型签名为 (T1, T2, ...) 的值，其中 T1、T2 是其成员的类型。函数可以使用元组返回多个值，因为元组可以容纳任意数量的值。

// Tuples can be used as function arguments and as return values.
fn reverse(pair: (i32, bool)) -> (bool, i32) {
    // `let` can be used to bind the members of a tuple to variables.
    let (int_param, bool_param) = pair;

    (bool_param, int_param)
}

// The following struct is for the activity.
#[derive(Debug)]
struct Matrix(f32, f32, f32, f32);

fn main() {
    // A tuple with a bunch of different types.
    let long_tuple = (1u8, 2u16, 3u32, 4u64,
                      -1i8, -2i16, -3i32, -4i64,
                      0.1f32, 0.2f64,
                      'a', true);

    // Values can be extracted from the tuple using tuple indexing.
    println!("Long tuple first value: {}", long_tuple.0);
    println!("Long tuple second value: {}", long_tuple.1);

    // Tuples can be tuple members.
    let tuple_of_tuples = ((1u8, 2u16, 2u32), (4u64, -1i8), -2i16);

    // Tuples are printable.
    println!("tuple of tuples: {:?}", tuple_of_tuples);

    // But long Tuples (more than 12 elements) cannot be printed.
    //let too_long_tuple = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13);
    //println!("Too long tuple: {:?}", too_long_tuple);
    // TODO ^ Uncomment the above 2 lines to see the compiler error

    let pair = (1, true);
    println!("Pair is {:?}", pair);

    println!("The reversed pair is {:?}", reverse(pair));

    // To create one element tuples, the comma is required to tell them apart
    // from a literal surrounded by parentheses.
    println!("One element tuple: {:?}", (5u32,));
    println!("Just an integer: {:?}", (5u32));

    // Tuples can be destructured to create bindings.
    let tuple = (1, "hello", 4.5, true);

    let (a, b, c, d) = tuple;
    println!("{:?}, {:?}, {:?}, {:?}", a, b, c, d);

    let matrix = Matrix(1.1, 1.2, 2.1, 2.2);
    println!("{:?}", matrix);
}

活动

1. 回顾：将 fmt::Display trait 添加到上面示例中的 Matrix 结构体中，这样如果您从打印调试格式 {:?} 切换到显示格式 {}，您将看到以下输出

   ( 1.1 1.2 )
   ( 2.1 2.2 )
   

   您可能需要参考打印显示的示例。

2. 使用 reverse 函数作为模板添加一个 transpose 函数，该函数接受一个矩阵作为参数，并返回一个交换了两个元素的矩阵。例如

   println!("Matrix:\n{}", matrix);
   println!("Transpose:\n{}", transpose(matrix));

   结果输出

   Matrix:
   ( 1.1 1.2 )
   ( 2.1 2.2 )
   Transpose:
   ( 1.1 2.1 )
   ( 1.2 2.2 )