temperature.rs

extern crate temperature;
use temperature::{Celsius, Fahrenheit, Kelvin, Rankine};
use std::str::FromStr;

macro_rules! temp_conv {
    ($fm:ident, $to:ident, $tmp:expr) => {
        let res = $fm::from_str($tmp); 
        match res {
            Ok(t) => {
                println!("{}", $to::from(t));   // never an arror
            },
            Err(e) =>{ println!("{}", e) }      //ParseFloatError || BelowAbsoluteZeroError
        }
    }
}
/*
macro_rules! map_sym {
    ($($sym:expr), +) => {
        {
            let mut x: Vec<&str> = Vec::new();
            $(
                match $sym {
                    "C" => x.push("Celsius"),
                    "F" => x.push("Fahrenheit"),
                    "K" => x.push("Kelvin"),
                    "R" => x.push("Rankine"),
                    _ => unreachable!()
                }   
            )+
            x
        };
    }
}
*/
fn main() {
    let args: Vec<String> = std::env::args().collect();
    let temp: &str = args[1].as_ref();
    let from: &str = args[2].as_ref();
    let to: &str = args[3].as_ref();

//    let fmto = map_sym!(from, to);
//    temp_conv![fmto[0], fmto[1], temp];
    match (from, to) {
        ("C", "F") => { temp_conv!(Celsius, Fahrenheit, temp); },
        ("C", "F") => { temp_conv!(Celsius, Fahrenheit, temp); },
        ("C", "K") => { temp_conv!(Celsius, Kelvin, temp); },
        ("C", "R") => { temp_conv!(Celsius, Rankine, temp); },
        ("F", "C") => { temp_conv!(Fahrenheit, Celsius, temp); },
        ("F", "K") => { temp_conv!(Fahrenheit, Kelvin, temp); },
        ("F", "R") => { temp_conv!(Fahrenheit, Rankine, temp); },
        ("K", "C") => { temp_conv!(Kelvin, Celsius, temp); },
        ("K", "F") => { temp_conv!(Kelvin, Fahrenheit, temp); },
        ("K", "R") => { temp_conv!(Kelvin, Rankine, temp); },
        ("R", "C") => { temp_conv!(Rankine, Celsius, temp); },
        ("R", "F") => { temp_conv!(Rankine, Fahrenheit, temp); },
        ("R", "K") => { temp_conv!(Rankine, Kelvin, temp); },
        _ => println!("Temperature unit unknown or feature not implemented. Valid units {{C|F|K|R}}\nExample: ./temperature 32 F C")
   };
}