Convenient Rust wrappers for a couple WinAPI calls

enum_windows.rs

pub fn enumerate_windows<F>(mut callback: F)
    where F: FnMut(HWND) -> bool
{
    let mut trait_obj: &mut FnMut(HWND) -> bool = &mut callback;
    let closure_pointer_pointer: *mut c_void = unsafe { mem::transmute(&mut trait_obj) };

    let lparam = closure_pointer_pointer as LPARAM;
    unsafe { EnumWindows(Some(enumerate_callback), lparam) };
}

pub fn enumerate_child_windows<F>(hwnd: HWND, mut callback: F)
    where F: FnMut(HWND) -> bool
{
    let mut trait_obj: &mut FnMut(HWND) -> bool = &mut callback;
    let closure_pointer_pointer: *mut c_void = unsafe { mem::transmute(&mut trait_obj) };

    let lparam = closure_pointer_pointer as LPARAM;
    unsafe { EnumChildWindows(hwnd, Some(enumerate_callback), lparam) };
}

unsafe extern "system" fn enumerate_callback(hwnd: HWND, lparam: LPARAM) -> BOOL {
    let closure: &mut &mut FnMut(HWND) -> bool = mem::transmute(lparam as *mut c_void);
    if closure(hwnd) { TRUE } else { FALSE }
}