Arc::new() lifetime error

gistfile1.rs

    fn it_works() {
        let guards: Vec<thread::JoinGuard<()>> = Vec::with_capacity(3);
        {
            let mut pool = ScopedThreadPool::new(2);

            for _ in (0..3) {
                guards.push(pool.execute(move || {
                    thread::sleep_ms(1000);
                    println!("Things are happening!");
                }));
            }
        }
        println!("Still running");


Errors with:

   Compiling threadpool v0.0.1 (file:///home/user/bbatha/projects/threadpool-rs)
src/lib.rs:42:17: 42:23 error: cannot borrow immutable local variable `guards` as mutable
src/lib.rs:42                 guards.push(pool.execute(move || {
                              ^~~~~~
src/lib.rs:42:29: 42:33 error: `pool` does not live long enough
src/lib.rs:42                 guards.push(pool.execute(move || {
                                          ^~~~
src/lib.rs:36:19: 49:6 note: reference must be valid for the block at 36:18...
src/lib.rs:36     fn it_works() {
src/lib.rs:37         let guards: Vec<thread::JoinGuard<()>> = Vec::with_capacity(3);
src/lib.rs:38         {
src/lib.rs:39             let mut pool = ScopedThreadPool::new(2);
src/lib.rs:40
src/lib.rs:41             for _ in (0..3) {
              ...
src/lib.rs:39:53: 47:10 note: ...but borrowed value is only valid for the block suffix following statement 0 at 39:52
src/lib.rs:39             let mut pool = ScopedThreadPool::new(2);
src/lib.rs:40
src/lib.rs:41             for _ in (0..3) {
src/lib.rs:42                 guards.push(pool.execute(move || {
src/lib.rs:43                     thread::sleep_ms(1000);
src/lib.rs:44                     println!("Things are happening!");