Add more Zeroable and ZeroableInOption impls (#158)

src/zeroable.rs

@@ -53,8 +53,17 @@ unsafe impl Zeroable for f64 {}
 unsafe impl<T: Zeroable> Zeroable for Wrapping<T> {}
 unsafe impl<T: Zeroable> Zeroable for core::cmp::Reverse<T> {}
 
+// Note: we can't implement this for all `T: ?Sized` types because it would
+// create NULL pointers for vtables.
+// Maybe one day this could be changed to be implemented for
+// `T: ?Sized where <T as core::ptr::Pointee>::Metadata: Zeroable`.
 unsafe impl<T> Zeroable for *mut T {}
 unsafe impl<T> Zeroable for *const T {}
+unsafe impl<T> Zeroable for *mut [T] {}
+unsafe impl<T> Zeroable for *const [T] {}
+unsafe impl Zeroable for *mut str {}
+unsafe impl Zeroable for *const str {}
+
 unsafe impl<T: Zeroable> Zeroable for PhantomData<T> {}
 unsafe impl Zeroable for PhantomPinned {}
 unsafe impl<T: Zeroable> Zeroable for ManuallyDrop<T> {}

src/zeroable_in_option.rs

@@ -25,4 +25,10 @@ unsafe impl ZeroableInOption for NonZeroU64 {}
 unsafe impl ZeroableInOption for NonZeroU128 {}
 unsafe impl ZeroableInOption for NonZeroUsize {}
 
-unsafe impl<T> ZeroableInOption for NonNull<T> {}
+// Note: this does not create NULL vtable because we get `None` anyway.
+unsafe impl<T: ?Sized> ZeroableInOption for NonNull<T> {}
+unsafe impl<T: ?Sized> ZeroableInOption for &'_ T {}
+unsafe impl<T: ?Sized> ZeroableInOption for &'_ mut T {}
+
+#[cfg(feature = "extern_crate_alloc")]
+unsafe impl<T: ?Sized> ZeroableInOption for alloc::boxed::Box<T> {}