A macro to easily create and populate hash maps.

hashmap-macro.rs

#![feature(macro_rules)]

extern crate collections;

use collections::HashMap;

// A macro to easily create and populate hash maps
macro_rules! hashmap(
    { $($key:expr => $value:expr),+ } => {
        {
            let mut m = HashMap::new();
            $(
                m.insert($key, $value);
            )+
            m
        }
    };
    ($hm:ident, { $($key:expr => $value:expr),+ } ) => (
        {
            $(
                $hm.insert($key, $value);
            )+
        }
    );
)

fn main() {

    // Create a new hashmap
    let mut hm = hashmap! {
        "a string"        => 21,
        "another string"  => 33
    };

    // Can also insert into it
    // the usual way
    hm.insert("and another", 43);

    // or also use the macro with
    // an existing hashmap
    hashmap!(hm, {
        "hey, look!" => 56,
        "even more"  => 77
    });

    for (k, v) in hm.iter() {
        println!("({}, {})", *k, *v);
    }
}

-> % rust run hash-macro.rs
("another string", 33)
("and another", 43)
("even more", 77)
("a string", 21)
("hey, look!", 56)