Exploring Rust Tuples and Transposing Matrices

Introduction

In this lab, we explore tuples in Rust. Tuples are collections of values of different types and are constructed using parentheses. They can be used as function arguments and return values, allowing functions to return multiple values. Tuples can also be used as members of other tuples. Rust provides tuple indexing to access values in a tuple. Tuples are printable and can be destructured to create bindings. Additionally, we learn how to add the fmt::Display trait to a struct to customize its printing format. Finally, we are given an activity to implement a transpose function that swaps two elements in a matrix.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

Skills Graph

Tuples

A tuple is a collection of values of different types. Tuples are constructed using parentheses (), and each tuple itself is a value with type signature (T1, T2, ...), where T1, T2 are the types of its members. Functions can use tuples to return multiple values, as tuples can hold any number of values.

// 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);
}

Activity

1. Recap: Add the fmt::Display trait to the Matrix struct in the above example, so that if you switch from printing the debug format {:?} to the display format {}, you see the following output:

   ( 1.1 1.2 )
   ( 2.1 2.2 )

   You may want to refer back to the example for print display.

2. Add a transpose function using the reverse function as a template, which accepts a matrix as an argument, and returns a matrix in which two elements have been swapped. For example:

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

   Results in the output:

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

Summary

Congratulations! You have completed the Tuples lab. You can practice more labs in LabEx to improve your skills.