gistfile1.rs

pub trait Entity {
	// ... some irrelevant functions
}

impl<'a> AnyRefExt<'a> for &'a ~Entity {
    #[inline]
    fn is<T: 'static>(self) -> bool {
        // Get TypeId of the type this function is instantiated with
        let t = TypeId::of::<T>();

        // Get TypeId of the type in the trait object
        let boxed = self.get_type_id();

        // Compare both TypeIds on equality
        t == boxed
    }

    #[inline]
    fn as_ref<T: 'static>(self) -> Option<&'a T> {
        if self.is::<T>() {
            Some(unsafe { transmute(self.as_void_ptr()) })
        } else {
            None
        }
    }
}

// In my enemy implementation, I want to find the player from a ~[~Entity] vector (which contains all enemies and the player). Like this:

impl Entity for Enemy {
	fn update(&self, dt: f32, world: &World, _input: &Input) -> UpdateResult {
		let player_entity = match world.entities.iter().find(|&e| (*e).is::<~Player>()) {
			Some(player) => player.as_ref::<~Player>(),
			None => fail!("No player found in world.")
		};

    // irrelevant code removed
	}
}