1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
use specs::prelude::*;
struct Pos(f32);
impl Component for Pos {
type Storage = VecStorage<Self>;
}
fn main() {
let mut world = World::new();
world.register::<Pos>();
let entity0 = world.create_entity().with(Pos(0.0)).build();
world.create_entity().with(Pos(1.6)).build();
world.create_entity().with(Pos(5.4)).build();
let mut pos = world.write_storage::<Pos>();
let entities = world.entities();
// Unlike `join` the type return from `lend_join` does not implement
// `Iterator`. Instead, a `next` method is provided that only allows one
// element to be accessed at once.
let mut lending = (&mut pos).lend_join();
// We copy the value out here so the borrow of `lending` is released.
let a = lending.next().unwrap().0;
// Here we keep the reference from `lending.next()` alive, so `lending`
// remains exclusively borrowed for the lifetime of `b`.
let b = lending.next().unwrap();
// This right fails to compile since `b` is used below:
// let d = lending.next().unwrap();
b.0 = a;
// Items can be iterated with `while let` loop:
let mut lending = (&mut pos).lend_join();
while let Some(pos) = lending.next() {
pos.0 *= 1.5;
}
// A `for_each` method is also available:
(&mut pos).lend_join().for_each(|pos| {
pos.0 += 1.0;
});
// Finally, there is one bonus feature which `.join()` can't soundly provide.
let mut lending = (&mut pos).lend_join();
// That is, there is a method to get the joined result for a particular
// entity:
if let Some(pos) = lending.get(entity0, &entities) {
pos.0 += 5.0;
}
}