# 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 (integer, boolean) = pair;

        (boolean, integer)
    }

    // 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 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 )