main() {
    Arena1 := Standard.Memory.Arena();
    v1 := Standard.Containers.Vector(int, Standard.Memory.ArenaAllocator)(alloc := arena1);
    {
        Arena2 := Standard.Memory.Arena();
        v2 = Standard.Containers.Vector(int, Standard.Memory.ArenaAllocator)(alloc := arena2);
        // fill v2 here
        v1 = v2;
    }
    // now what?
}