Add ZeroVec::owned_capacity (#3431)

utils/zerovec/src/zerovec/mod.rs

@@ -20,6 +20,7 @@ use core::fmt;
 use core::iter::FromIterator;
 use core::marker::PhantomData;
 use core::mem;
+use core::num::NonZeroUsize;
 use core::ops::Deref;
 
 /// A zero-copy, byte-aligned vector for fixed-width types.
@@ -554,6 +555,34 @@ where
  Some(ZeroSlice::from_ule_slice(ule_slice))
  }
  }
+
+ /// If the ZeroVec is owned, returns the capacity of the vector.
+ ///
+ /// Otherwise, if the ZeroVec is borrowed, returns `None`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use zerovec::ZeroVec;
+ ///
+ /// let mut zv = ZeroVec::<u8>::new_borrowed(&[0, 1, 2, 3]);
+ /// assert!(!zv.is_owned());
+ /// assert_eq!(zv.owned_capacity(), None);
+ ///
+ /// // Convert to owned without appending anything
+ /// zv.with_mut(|v| ());
+ /// assert!(zv.is_owned());
+ /// assert_eq!(zv.owned_capacity(), Some(4.try_into().unwrap()));
+ ///
+ /// // Double the size by appending
+ /// zv.with_mut(|v| v.push(0));
+ /// assert!(zv.is_owned());
+ /// assert_eq!(zv.owned_capacity(), Some(8.try_into().unwrap()));
+ /// ```
+ #[inline]
+ pub fn owned_capacity(&self) -> Option<NonZeroUsize> {
+ NonZeroUsize::try_from(self.vector.capacity).ok()
+ }
 }
 
 impl<'a> ZeroVec<'a, u8> {