Macro try_vec_in 

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

Creates a Vec containing the arguments with the provided allocator.

try_vec_in! allows Vecs 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:

#![feature(allocator_api)]
use std::alloc::System;

let v = try_vec_in![1, 2, 3 => System]?;
assert_eq!(v[0], 1);
assert_eq!(v[1], 2);
assert_eq!(v[2], 3);

• Create a Vec from a given element and size:

#![feature(allocator_api)]
use std::alloc::System;

let v = try_vec_in![1; 3 => System]?;
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, try_ve_in![Rc::new(1); 5 => allocator] will create a vector of five references to the same boxed integer value, not five references pointing to independently boxed integers.

Also, note that try_vec_in![expr; 0 => allocator] 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.