Macros with repetition in Rust

Repetition captures a list, so one macro builds a whole collection.

use std::collections::HashMap;

macro_rules! table {
    ($($key:expr => $value:expr),* $(,)?) => {{
        let mut map = HashMap::new();
        $(map.insert($key, $value);)*
        map
    }};
}

macro_rules! log_all {
    ($($line:expr);*) => {
        $(println!("[log] {}", $line);)*
    };
}

fn main() {
    let tours = table! {
        "rust" => 11,
        "python" => 6,
    };
    println!("{}", tours["rust"]);

    log_all!("started"; "finished");
}

How it works

1. $( ... ),* matches a comma-separated list.
2. The body repeats once per captured item.
3. This is how vec! and hashmap! style macros work.

Keywords and builtins used here

• expr
• fn
• let
• main
• mut
• use

The run, in numbers

Lines

25

Characters to type

384

Tokens

142

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 77 seconds.

Type this snippet

Step 3 of 3 in Macros, step 9 of 12 in Modules, tests & macros.

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