Add clone_from implementations

src/array.rs

@@ -167,6 +167,14 @@ impl<T: Clone, LenT: ValidLength> Clone for FixedArray<T, LenT> {
         // SAFETY: The Box::from cannot make the length mismatch.
         unsafe { Self::from_box_with_nonzero(ptr, self.len) }
     }
+
+    fn clone_from(&mut self, source: &Self) {
+        if self.len() == source.len() {
+            self.clone_from_slice(source);
+        } else {
+            *self = source.clone();
+        }
+    }
 }
 
 impl<T, LenT: ValidLength> core::ops::Index<LenT> for FixedArray<T, LenT> {

src/string.rs

@@ -162,6 +162,13 @@ impl<LenT: ValidLength> Clone for FixedString<LenT> {
             FixedStringRepr::Static(a) => Self(FixedStringRepr::Static(*a)),
         }
     }
+
+    fn clone_from(&mut self, source: &Self) {
+        match (&mut self.0, &source.0) {
+            (FixedStringRepr::Heap(new), FixedStringRepr::Heap(src)) => new.clone_from(src),
+            _ => *self = source.clone(),
+        }
+    }
 }
 
 impl<LenT: ValidLength> Hash for FixedString<LenT> {