Example of simple slow build for slack-rs

main.rs

extern crate slack;
extern crate rustc_serialize;

use rustc_serialize::json;
use slack::api::*;

struct MyHandler {
    count: i64,
}

#[allow(unused_variables)]
impl slack::EventHandler for MyHandler {
    fn on_receive(&mut self, cli: &mut slack::RtmClient, json_str: &str) {
        self.count += 1;

        // Below line makes cargo build --release go from 5 seconds to 66 (after intial really slow one)
        json::decode::<MessageEvent>(json_str);
    }

    fn on_ping(&mut self, cli: &mut slack::RtmClient) { }
    fn on_close(&mut self, cli: &mut slack::RtmClient) { }
    fn on_connect(&mut self, cli: &mut slack::RtmClient) { }
}

fn main() {
    let mut handler = MyHandler { count: 0 };
    let mut cli = slack::RtmClient::new("blah-blah-blah");
    let _ = cli.login_and_run::<MyHandler>(&mut handler);
}