alloc

# Macro vec

1.36.0 · Source

    macro_rules! vec {
        () => { ... };
        ($elem:expr; $n:expr) => { ... };
        ($($x:expr),+ $(,)?) => { ... };
    }

Expand description

Creates a `Vec` containing the arguments.

`vec!` allows `Vec`s to be defined with the same syntax as array expressions. There are two forms of this macro:

- Create a `Vec` containing a given list of elements:

    let v = vec![1, 2, 3];
    assert_eq!(v[0], 1);
    assert_eq!(v[1], 2);
    assert_eq!(v[2], 3);

- Create a `Vec` from a given element and size:

    let v = vec![1; 3];
    assert_eq!(v, [1, 1, 1]);

Note that unlike array expressions this syntax supports all elements which implement `Clone` and the number of elements doesn’t have to be a constant.

This will use `clone` to duplicate an expression, so one should be careful using this with types having a nonstandard `Clone` implementation. For example, `vec![Rc::new(1); 5]` will create a vector of five references to the same boxed integer value, not five references pointing to independently boxed integers.

Also, note that `vec![expr; 0]` is allowed, and produces an empty vector. This will still evaluate `expr`, however, and immediately drop the resulting value, so be mindful of side effects.