MapMacro.rs

#![feature(macro_rules)]

use std::collections::HashMap;

macro_rules! map(
    { $T:ident $($args:tt)* } => {
        {
            let mut m = $T::new();
            map_insert! { m $($args)* }
        }
    }
)
    
macro_rules! map_insert(
    { $m:expr } => { { $m } };
    { $m:expr, } => { { $m } };
    { $m:expr, $key:expr => $value:expr $($args:tt)* } => {
        {
            $m.insert($key, $value);
            map_insert! { $m $($args)* }
        }
    };
    { $m:expr, $key:ident: $value:expr $($args:tt)* } => {
        {
            $m.insert(stringify!($key), $value);
            map_insert! { $m $($args)* }
        }
    };
)

fn main() {
    let pi = "\u03c0";
    let m = map! { HashMap,
        the_answer: 42.0f32,
        pi => 3.14159f32,
        "e" => 2.71828f32
    };
    println!("{}", m);
}