Code shared from the Rust Playground

playground.rs

extern crate futures; // 0.1.25
use futures::prelude::*;
use futures::future::{ok, err};

pub struct Boop {}

pub enum Cmd {
    a,
    b
}

impl Boop {
    pub fn a(&mut self, ) -> impl Future<Item=(), Error=()> {
        ok(())
    }
    
    pub fn b(&mut self, ) -> impl Future<Item=(), Error=()> {
        ok(())
    }
    
    pub fn exec(&mut self, cmd: Cmd) -> impl Future<Item=(), Error=()> {
        match cmd {
            Cmd::a => self.a(),
            Cmd::b => self.b(),
        }
    }
}



fn main() {
    let mut b = Boop{};
    
    b.a().wait().unwrap();
    b.b().wait().unwrap();
    b.exec(Cmd::a).wait().unwrap();
    b.exec(Cmd::b).wait().unwrap();
}