Macro velcro::vec

vec!() { /* proc-macro */ }

A more flexible vector initialization macro. velcro::vec! is a drop-in replacement for the built-in std::vec! macro, but with extra functionality. In particular, it adds the .. spread operator, which can insert multiple elements at once, provided that the expression implements IntoIterator, which is the case for all iterators and most collections.

Usage

use velcro::vec;

assert_eq!(vec![..(0..7)], vec![0, 1, 2, 3, 4, 5, 6]);
assert_eq!(vec![0, 1, ..(2..7)], vec![0, 1, 2, 3, 4, 5, 6]);

let other = vec![3, 4, 5];
assert_eq!(vec![0, 1, 2, ..other, 6], vec![0, 1, 2, 3, 4, 5, 6]);

let mut it = (0..=3).into_iter().map(|x| x + 2);
assert_eq!(vec![0, 1, ..it, 6], vec![0, 1, 2, 3, 4, 5, 6]);

assert_eq!(vec![3; 5], vec![3, 3, 3, 3, 3]);
let range = 3..;
assert_eq!(vec![..range; 5], vec![3, 4, 5, 6, 7]);
// Note that this is different from not using `..`
let range = 3..;
assert_eq!(vec![range; 5], vec![3.., 3.., 3.., 3.., 3..]);

// If the requested length is less than the input length then the
// result will be shorter.
let range = 2..5;
assert_eq!(vec![..range; 5], vec![2, 3, 4]);

Performance

For syntax that is supported by std::vec!, velco::vec! performs the same, since it delegates to std::vec! wherever the input is compatible. That is, if you don’t use the .. spread operator, you don’t pay for it.