Add zero_filled constructor

src/array_string.rs

@@ -129,6 +129,28 @@ impl<const CAP: usize> ArrayString<CAP>
         Ok(vec)
     }
 
+    /// Creates a new `ArrayString` instance fully filled with ASCII NULL characters (`\0`). Useful
+    /// to be used as buffer to collect external data or as an buffer for intermediate processing.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let string = ArrayString::<16>::zero_filled();
+    /// assert_eq!(string.len(), 16);
+    /// ```
+    #[inline]
+    pub fn zero_filled() -> Self {
+        let mut vec = Self::new();
+        let data = [b'\0'; CAP];
+        // SAFETY: The array is fully filled with valid UTF-8
+        unsafe {
+            let ptr = data.as_ptr() as *const [MaybeUninit<u8>; CAP];
+            ptr.copy_to_nonoverlapping(&mut vec.xs as *mut _, 1);
+            vec.set_len(CAP);
+        }
+        vec
+    }
+
     /// Return the capacity of the `ArrayString`.
     ///
     /// ```

tests/tests.rs

@@ -773,7 +773,6 @@ fn test_arrayvec_const_constructible() {
     assert_eq!(var[..], [vec![3, 5, 8]]);
 }
 
-
 #[test]
 fn test_arraystring_const_constructible() {
     const AS: ArrayString<10> = ArrayString::new_const();
@@ -786,3 +785,9 @@ fn test_arraystring_const_constructible() {
 }
 
 
+#[test]
+fn test_array_string_has_some_sanity_checks() {
+    let string = ArrayString::<4>::zero_filled();
+    assert_eq!(string.as_str(), "\0\0\0\0");
+    assert_eq!(string.len(), 4);
+}