How to pass a null ptr to some functions?

[hicqu]

look at this function:

fn epoll_ctl(epfd: RawFd, op: EpollOp, fd: RawFd, event: &mut EpollEvent)

if EpollOp == EpollDel, the event could be a NULL in C. But how to pass a NULL ptr to epoll_ctl in rust?

[fiveop]

This is a missing feature of our interface. We had a similar problem with kill (see #445). Feel free to create a PR to fix this. We will incorporate it, even if it is a breaking change. We should probably check in the new implementation of epoll_ctl, whether event may be None (or NULL in C) depending on the other arguments.

[hicqu]

OK, I think we can define these two functions in mio. Here is a simple test:

/// maybe we could accept these two functions into mio?
fn null_as_mut<T>() -> &'static mut T {
    unsafe { &mut *::std::ptr::null_mut::<T>() }
}

fn null_as_ref<T>() -> &'static T {
    unsafe { & *::std::ptr::null::<T>() }
}

/// simple test below

#[derive(Debug)]
struct T { f: i32, }

fn ref_t(t: &T) {
    // if pass nullptr, segment fault as expected.
    println!("{:?}", *t);   
}

fn mut_t(t: &mut T) {
    // if pass nullptr, segment fault as expected.
    println!("{:?}", *t);   
}

fn main() {
    let mut t: T = T { f: 100 };
    ref_t(&t);  // it's OK.

    mut_t(null_as_mut::<T>());  // segment fault.
    ref_t(null_as_ref::<T>());  // segment fault.
}

What do you think?