wiki/content/20200915140449-vectors.md

---
date: 2020-09-15
id: 2eec2c96-e006-4a53-b5cc-fd39f466a6b7
title: Rust Vectors
---

# Traits

## std

### convert

-   [TryInto](20201119171245-tryinto)

# Description

Vectors allow you to store more than one value in a single data
structure that puts all the values next to each other in memory. Vectors
can only store values of the same type. They are useful when you have a
list of items, such as the lines of text in a file or the prices of
items in a shopping cart.

# Creating a New Vector

``` rust
fn main() {
    let v: Vec<i32> = Vec::new();
}
```

## vec! macro

Rust can often infer the type of value you want to store in the Vector.
For convenience one can also use the [vec!
macro](https://doc.rust-lang.org/std/macro.vec.html).

``` rust
fn main() {
    let v = vec![1, 2, 3];
}
```

# Updating a Vector

``` rust
fn main() {
    let mut v = Vec::new();

    v.push(5);
    v.push(6);
    v.push(7);
    v.push(8);
}
```

# Dropping a Vector

Like other [structs](20200831193417-structs), vectors are freed when
they go out of scope, along with the vector contents:

``` rust
fn main() {
    {
        let v = vec![1, 2, 3, 4];

        // do stuff with v
    } // <- v goes out of scope and is freed here
}
```

# Read Vector elements

There are two ways to reference a value stored in a vector:

``` rust
fn main() {
    let v = vec![1, 2, 3, 4, 5];

    let third: &i32 = &v[2];
    println!("The third element is {}", third);

    match v.get(2) {
        Some(third) => println!("The third element is {}", third),
        None => println!("There is no third element."),
    }
}
```

Using
[get](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.get)
together with
[match](https://doc.rust-lang.org/rust-by-example/flow_control/match.html)
seems preferable, as trying to get non existant elements with method \#1
will cause an \`index out of bounds\` panic:

``` rust
fn main() {
    let v = vec![1, 2, 3, 4, 5];

    let does_not_exist = &v[100];
    let does_not_exist = v.get(100);
}
```

When the `get` method is passed an index that is outside the vector, it
returns `None` without panicking.

# Iteration

## Immutable references

``` rust
fn main() {
    let v = vec![100, 32, 57];
    for i in &v {
        println!("{}", i);
    }
}
```

## Mutable references

``` rust
fn main() {
    let mut v = vec![100, 32, 57];
    for i in &mut v {
        *i += 50;
    }
}
```

# Using Enums to store multiple types

``` rust
fn main() {
    enum SpreadsheetCell {
        Int(i32),
        Float(f64),
        Text(String),
    }

    let row = vec![
        SpreadsheetCell::Int(3),
        SpreadsheetCell::Text(String::from("blue")),
        SpreadsheetCell::Float(10.12),
    ];
}
```