`Tuple`

Often in Rust we need to store related values together. Here a tuple can be ideal—it cannot be appended to, but we can store many together in a list.

For accessing tuple items, we use a number property. This is different from arrays or vectors. We also find that tuples can be pretty-printed with println.

Simple example

When we create a tuple, we usually do not need to specify the type. Here we create a tuple with 3 items: a string, integer and bool.

fn main() {
    // Create tuple.
    let value = ("bird", 100, false);

    // Print all tuple items.
    println!("{:?}", value);

    // Print first item.
    let first_item = value.0;
    println!("{}", first_item);
}("bird", 100, false)
bird

Complex example

Continuing on, we have a more complex example where we create a vector (list) of tuples. The tuples each have a string and integer in them.

Part 1 We access the first tuple in the list of tuples. Here we see the type of the tuple, and how to specify it in a variable.

Part 2 We get the first item in a tuple by using the "0" property. We print the result to the screen.

Part 3 We add a tuple to the Vector of tuples. We call push(). Please notice how the list has the mut keyword, meaning it can be mutated.

Part 4 Here we loop over the tuples in our vector. This shows each key and value—which are the item 0 and item 1 parts of the tuple.

fn main() {
    let mut list = vec![("bird", 10), ("cat", 20)];

    // Part 1: get first tuple from vector.
    let first_items: (&str, i32) = list[0];
    println!("{:#?}", first_items);

    // Part 2: get item from first tuple.
    let first = first_items.0;
    println!("{}", first);

    // Part 3: add a value to the vector, printing it before and after.
    println!("BEFORE: {:#?}", list);
    list.push(("tree", 5));
    println!("AFTER: {:#?}", list);

    // Part 4: loop over tuples in vector.
    for (a, b) in list {
        println!("A: {}", a);
        println!("B: {}", b);
    }
}(
    "bird",
    10,
)
bird
BEFORE: [
    (
        "bird",
        10,
    ),
    (
        "cat",
        20,
    ),
]
AFTER: [
    (
        "bird",
        10,
    ),
    (
        "cat",
        20,
    ),
    (
        "tree",
        5,
    ),
]
A: bird
B: 10
A: cat
B: 20
A: tree
B: 5

Return multiple values

This Rust example uses more complex tuple syntax. We return a tuple from a function. In get_color_and_id we use a match expression to return a tuple based on the argument.

And In main() we call the get_color_and_id function. We can access the 0 and 1 fields, or assign directly to them from the tuple result.

fn get_color_and_id(index: usize) -> (String, i32) {
    match index {
        1 | 2 => ("blue".to_string(), 2),
        _ => ("red".to_string(), 10),
    }
}

fn main() {
    // Get tuple, and then access its 0 and 1 fields.
    let result = get_color_and_id(0);
    println!("{} {}", result.0, result.1);

    // Get parts of tuple directly in assignment.
    let (color, id) = get_color_and_id(2);
    println!("{} {}", color, id);
}red 10
blue 2

`Tuple` argument

A tuple can be passed to a function. Tuples are always copied by value, much like an integer value. Here we pass a tuple to handle_tuple.

Note We can take a reference to a tuple and pass that to a function. The ampersand operator is used.

fn handle_tuple(t: (usize, &str, u8)) {
    println!("{}, str = {}", t.0 + (t.2 as usize), t.1);
}

fn main() {
    let tuple = (100000, "RUST", 3);
    // Pass tuple value.
    handle_tuple(tuple);
}
100003, str = RUST

Tuples are used throughout Rust programs—they are one of the foundational types. We can create and access them with a clear, simple syntax.

Tuple

Simple example

Complex example

Return multiple values

Tuple argument

`Tuple`

`Tuple` argument