# Macro std::vec 1.0.0[−][src]

```
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);
```

Run- Create a
`Vec`

from a given element and size:

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

RunNote 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.