src/doc/rust-by-example/src/primitives/tuples.md

   1 # Tuples
   2
   3 A tuple is a collection of values of different types. Tuples are constructed
   4 using parentheses `()`, and each tuple itself is a value with type signature
   5 `(T1, T2, ...)`, where `T1`, `T2` are the types of its members. Functions can
   6 use tuples to return multiple values, as tuples can hold any number of values.
   7
   8 ```rust,editable
   9 // Tuples can be used as function arguments and as return values
  10 fn reverse(pair: (i32, bool)) -> (bool, i32) {
  11     // `let` can be used to bind the members of a tuple to variables
  12     let (integer, boolean) = pair;
  13
  14     (boolean, integer)
  15 }
  16
  17 // The following struct is for the activity.
  18 #[derive(Debug)]
  19 struct Matrix(f32, f32, f32, f32);
  20
  21 fn main() {
  22     // A tuple with a bunch of different types
  23     let long_tuple = (1u8, 2u16, 3u32, 4u64,
  24                       -1i8, -2i16, -3i32, -4i64,
  25                       0.1f32, 0.2f64,
  26                       'a', true);
  27
  28     // Values can be extracted from the tuple using tuple indexing
  29     println!("long tuple first value: {}", long_tuple.0);
  30     println!("long tuple second value: {}", long_tuple.1);
  31
  32     // Tuples can be tuple members
  33     let tuple_of_tuples = ((1u8, 2u16, 2u32), (4u64, -1i8), -2i16);
  34
  35     // Tuples are printable
  36     println!("tuple of tuples: {:?}", tuple_of_tuples);
  37
  38     // But long Tuples (more than 12 elements) cannot be printed
  39     // let too_long_tuple = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13);
  40     // println!("too long tuple: {:?}", too_long_tuple);
  41     // TODO ^ Uncomment the above 2 lines to see the compiler error
  42
  43     let pair = (1, true);
  44     println!("pair is {:?}", pair);
  45
  46     println!("the reversed pair is {:?}", reverse(pair));
  47
  48     // To create one element tuples, the comma is required to tell them apart
  49     // from a literal surrounded by parentheses
  50     println!("one element tuple: {:?}", (5u32,));
  51     println!("just an integer: {:?}", (5u32));
  52
  53     //tuples can be destructured to create bindings
  54     let tuple = (1, "hello", 4.5, true);
  55
  56     let (a, b, c, d) = tuple;
  57     println!("{:?}, {:?}, {:?}, {:?}", a, b, c, d);
  58
  59     let matrix = Matrix(1.1, 1.2, 2.1, 2.2);
  60     println!("{:?}", matrix);
  61
  62 }
  63 ```
  64
  65 ### Activity
  66
  67  1. *Recap*: Add the `fmt::Display` trait to the `Matrix` struct in the above example,
  68     so that if you switch from printing the debug format `{:?}` to the display
  69     format `{}`, you see the following output:
  70
  71     ```text
  72     ( 1.1 1.2 )
  73     ( 2.1 2.2 )
  74     ```
  75
  76     You may want to refer back to the example for [print display][print_display].
  77  2. Add a `transpose` function using the `reverse` function as a template, which
  78     accepts a matrix as an argument, and returns a matrix in which two elements
  79     have been swapped. For example:
  80
  81     ```rust,ignore
  82     println!("Matrix:\n{}", matrix);
  83     println!("Transpose:\n{}", transpose(matrix));
  84     ```
  85
  86     results in the output:
  87
  88     ```text
  89     Matrix:
  90     ( 1.1 1.2 )
  91     ( 2.1 2.2 )
  92     Transpose:
  93     ( 1.1 2.1 )
  94     ( 1.2 2.2 )
  95     ```
  96
  97 [print_display]: ../hello/print/print_display.md