Dependencies include specs and specs-derive

specs-test.rs

use specs::prelude::*;
use specs_derive::*;

#[derive(Component)]
#[storage(VecStorage)]
struct Position {
    x: i32,
    y: i32,
}

struct Color(u8, u8, u8);

#[derive(Component)]
#[storage(VecStorage)]
struct Drawable {
    char: char,
    background_color: Color,
    foreground_color: Color,
}

#[derive(Component)]
#[storage(VecStorage)]
struct Health {
    max_health: i32,
    current_health: i32,
}

struct Draw;
impl<'a> System<'a> for Draw {
    type SystemData = (ReadStorage<'a, Position>, ReadStorage<'a, Drawable>);

    fn run(&mut self, (pos, drawable): Self::SystemData) {
        use specs::Join;

        for (pos, drawable) in (&pos, &drawable).join() {
            println!("{} at ({}, {})", drawable.char, pos.x, pos.y);
        }
    }
}

struct UpdatePos;
impl<'a> System<'a> for UpdatePos {
    type SystemData = WriteStorage<'a, Position>;

    fn run(&mut self, mut pos: Self::SystemData) {
        use specs::Join;

        for pos in (&mut pos).join() {
            pos.x += 1;
            pos.y += 1;
        }
    }
}

fn create_player(world: &mut World, char: char, pos: Position) {
    world.create_entity()
        .with(pos)
        .with(Health { max_health: 100, current_health: 100 })
        .with(Drawable { char, foreground_color: Color(0xff, 0xff, 0xff), background_color: Color(0, 0, 0)})
        .build();
}

fn main() {
    let mut world = World::new();
    // add these lines...
    // world.register::<Position>();
    // world.register::<Drawable>();
    // world.register::<Health>();

    let mut dispatcher = DispatcherBuilder::new()
        .with(UpdatePos, "update_pos", &[])
        .with(Draw, "draw", &["update_pos"])
        .build();

    dispatcher.setup(&mut world.res); // ...and comment out this line to make it work

    create_player(&mut world, '@', Position { x: 0, y: 0 });
    create_player(&mut world, 'T', Position { x: 0, y: 5 });

    for _ in 0 .. 10 {
        dispatcher.dispatch(&world.res);
        world.maintain();
    }
}