refcell.rs

use std::cell::RefCell;

enum Type {
    Add,
    Sub
}

struct Entity {
    t: Type,
    i: i32,
}

impl Entity {
    pub fn update(&self, own_id: usize, v: &Vec<RefCell<Entity>>){
        for i in 0..v.len() {
            if i == own_id {
                continue;
            }
            match self.t {
                Type::Add => {
                    let mut ti = v[i].borrow_mut();
                    ti.i = ti.i + 1;
                }
                Type::Sub => {
                    let mut ti = v[i].borrow_mut();
                    ti.i = ti.i - 1;
                }
            }
        }
    }
}

fn main() {

    let entities = vec![
        RefCell::new(Entity{t: Type::Add, i: 0}),
        RefCell::new(Entity{t: Type::Add, i: 0}),
        RefCell::new(Entity{t: Type::Add, i: 0}),
        RefCell::new(Entity{t: Type::Sub, i: 0}),
        RefCell::new(Entity{t: Type::Sub, i: 0}),
    ];

    for i in 0..entities.len() {
        let e = entities[i].borrow_mut();
        e.update(i, &entities);
        println!("[{}]: {}", i, e.i);
    }
}

/* OUTPUT

## before adding in the own_id check
$ cargo run
   Compiling rustscratch v0.1.0 (/home/byoung/tmp/rustscratch)
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s
     Running `target/debug/rustscratch`
thread 'main' panicked at src/main.rs:18:39:
already borrowed: BorrowMutError
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

## after adding in the own_id check
$ cargo run
   Compiling rustscratch v0.1.0 (/home/byoung/tmp/rustscratch)
    Finished dev [unoptimized + debuginfo] target(s) in 0.12s
     Running `target/debug/rustscratch`
[0]: 0
[1]: 1
[2]: 2
[3]: 3
[4]: 2

*/