How to use vec! macro in a #![no_std] library?

Question

In standard Rust code, the vec! macro is in the prelude and there is no need to make it visible manually. I'm working on a library that doesn't use the standard library and sets #![no_std] , so also the prelude isn't visible.

Inside the test code, I am using functionality from the standard library, therefore I have a

#[cfg(test)]
extern crate std;

This works without problems to access functions and datatypes from the standard library, but now I would like to access the vec!(...) macro and I don't know how.

use std::vec::vec!; results in an error:

expected one of `::`, `;`, or `as` here 

at the position of the exclamation mark.

How can I access this macro instead?

Answer 1

vec! is a macro so you have to add #[macro_use] :

#[cfg(test)]
#[macro_use]
extern crate std;

If you are on a nightly compiler, you can also use the use_extern_macros feature:

#![feature(use_extern_macros)]

#[cfg(test)]
extern crate std;

#[cfg(test)]
mod test {
    use std::vec;
}

Answer 2

In addition to Tims answer , if you have an embedded system and you have an allocator, but not std, you can use

#[macro_use]
extern crate alloc;

to be able to use vec!