add: extend_from_slice()

src/lib.rs

@@ -414,6 +414,13 @@ impl<H, T> HeaderVec<H, T> {
         unsafe { (self.ptr as *mut T).add(Self::offset()) }
     }
 
+    /// Gets the pointer to the end of the slice. This returns a mutable pointer to
+    /// uninitialized memory behind the last element.
+    #[inline(always)]
+    fn end_ptr_mut(&mut self) -> *mut T {
+        unsafe { self.start_ptr_mut().add(self.len_exact())}
+    }
+
     #[inline(always)]
     fn header(&self) -> &HeaderVecHeader<H> {
         // The beginning of the memory is always the header.
@@ -427,6 +434,28 @@ impl<H, T> HeaderVec<H, T> {
     }
 }
 
+impl<H, T: Clone> HeaderVec<H, T> {
+    /// Adds items from a slice to the end of the list.
+    ///
+    /// Returns `Some(*const ())` if the memory was moved to a new location.
+    /// In this case, you are responsible for updating the weak nodes.
+    pub fn extend_from_slice(&mut self, slice: &[T]) -> Option<*const ()> {
+        let previous_pointer = self.reserve(slice.len());
+
+        // copy data
+        let end_ptr = self.end_ptr_mut();
+        for (index, item) in slice.iter().enumerate() {
+            unsafe {
+                core::ptr::write(end_ptr.add(index), item.clone());
+            }
+        }
+        // correct the len
+        self.header_mut().len = (self.len_exact() + slice.len()).into();
+
+        previous_pointer
+    }
+}
+
 #[cfg(feature = "atomic_append")]
 /// The atomic append API is only enabled when the `atomic_append` feature flag is set (which
 /// is the default).

tests/simple.rs

@@ -53,3 +53,12 @@ fn test_push() {
     hv.push(123);
     assert_eq!(hv[0], 123);
 }
+
+#[test]
+fn test_extend_from_slice() {
+    let mut hv = HeaderVec::new(());
+
+    hv.extend_from_slice(&[0, 1, 2]);
+    hv.extend_from_slice(&[3, 4, 5]);
+    assert_eq!(hv.as_slice(), &[0, 1, 2, 3, 4, 5]);
+}