Short self contained test case demonstrating something I don't understand about rust.

test.rs

fn foo<T:Copy>(arr: ~[T]) -> ~[T] {
    ~[arr[0]]
}

fn main() {
    let bar = ~[1,2,3];
    for foo(bar).iter().advance |i| {
        println(fmt!("%?", i));
    }
}

traceback

> rust run test.rs
test.rs:8:8: 8:17 error: borrowed value does not live long enough
test.rs:8     for foo(bar).iter().advance |i| {
                  ^~~~~~~~~
test.rs:10:4: 10:5 note: borrowed pointer must be valid for the method call at 10:4...
test.rs:10     }
               ^
test.rs:8:8: 8:24 note: ...but borrowed value is only valid for the method call at 8:8
test.rs:8     for foo(bar).iter().advance |i| {
                  ^~~~~~~~~~~~~~~~
test.rs:8:12: 8:15 error: use of moved value: `bar`
test.rs:8     for foo(bar).iter().advance |i| {
                      ^~~
test.rs:7:27: 7:30 note: `bar` moved here because it has type `~[int]`, which is moved by default (use `copy` to override)
test.rs:7     println(fmt!("%?", foo(bar)));
                                     ^~~
note: in expansion of fmt!
test.rs:7:12: 7:33 note: expansion site
error: aborting due to 2 previous errors