Macro lit_vek::vek

source ·

macro_rules! vek {
    () => { ... };
    ($($tail:tt)*) => { ... };
}

Expand description

A drop-in replacement for vec![] that adds “spread” syntax.


let arr = [1, 2, 3];
let vec = vec![8, 9, 10];

assert_eq!(
    vek![...arr, 4, ...(5..7), 7, ...vec],
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

vek![a, b, c] simply returns a vec of those elements, exactly like vec!. But elements can be prefixed with ... to indicate a “spread”, which is expanded by calling into_iter().

Examples

Normal vec! syntax works the same way:

use lit_vek::vek;

assert_eq!(vek![1, 2, 3], vec![1, 2, 3]);
assert_eq!(vek!["x"; 5], vec!["x"; 5]);

Spread syntax [...xs] inserts xs into the result via into_iter():

use lit_vek::vek;
let abc = [1, 2, 3];

assert_eq!(vek![...abc, ...abc], [1, 2, 3, 1, 2, 3]);

You can also use [...xs; n] to repeat a sequence n times, like std::iter::cycle() but of finite length. The iterator returned by xs.into_iter() must implement Clone.

use lit_vek::vek;

let abc = [1, 2, 3];
assert_eq!(
    vek![...abc; 2], [1, 2, 3, 1, 2, 3])

And all these can be combined:

use lit_vek::vek;
let abc = [1, 2, 3];

// Note that (3..5) here is an ordinary range expression,
// not special syntax.
assert_eq!(
    vek![1, ...[2;2], ...[...(3..5);2]],
    [1, 2, 2, 3, 4, 3, 4]);

assert_eq!(
    vek![0, ...[...abc; 2], ...[9; 3]],
    [0, 1, 2, 3, 1, 2, 3, 9, 9, 9]);

The cycle-n-times logic is also available as a function, cycle_n since it’s missing from std::iterator.

Why ... when most range-like things in Rust, including the existing pattern spread syntax, use “..”? Because ..x is already an expression of type std::ops::RangeTo. The macro could still work with .., and you could disambiguiate by parenthesizing if necessary:

    let r = [..1, ..2];
    let my_ranges = vek![(..1), ..r];

But it seemed better to sidestep the issue.

Why prefix instead of suffix syntax, like vek![a, bs..., c]? Mostly to match other languages I’m aware of with spread syntax.

Macro lit_vek::vek

Examples

Design choices

See also