Default for AtomicPtr?

[njwhite]

Is there any reason why there isn't an ATOMIC_PTR_INIT (cf ATOMIC_BOOL_INIT, ATOMIC_ISIZE_INIT, &c.) struct? I'd like to use AtomicPtrs in statically-initialized variables - and AtomicPtr is the only atomic class that doesn't implement the Default trait. A std::ptr::null_mut() seems to be a sensible initial value.

[sfackler]

You can't define generic consts so ATOMIC_PTR_INIT can't be expressed. We can add a Default implementation though.

[steveklabnik]

/cc @aturon