Macro indexmap 

macro_rules! indexmap {
    ($($key:expr => $value:expr,)+) => { ... };
    ($($key:expr => $value:expr),*) => { ... };
}

Available on crate features map and std only.

Create an IndexMap from a list of key-value pairs

Example

use indexmap::indexmap;

let map = indexmap!{
    "a" => 1,
    "b" => 2,
};
assert_eq!(map["a"], 1);
assert_eq!(map["b"], 2);
assert_eq!(map.get("c"), None);

// "a" is the first key
assert_eq!(map.keys().next(), Some(&"a"));