add FixedArray::is_empty

builtin/builtin.mbti

@@ -695,6 +695,7 @@ impl FixedArray {
   default[X]() -> Self[X]
   fill[T](Self[T], T) -> Unit
   get[T](Self[T], Int) -> T
+  is_empty[T](Self[T]) -> Bool
   iter[T](Self[T]) -> Iter[T]
   iter2[T](Self[T]) -> Iter2[Int, T]
   length[T](Self[T]) -> Int

builtin/fixedarray.mbt

@@ -76,3 +76,26 @@ pub fn compare[T : Compare](self : FixedArray[T], other : FixedArray[T]) -> Int
     }
   }
 }
+
+///|
+/// Tests whether the FixedArray contains no elements.
+///
+/// Parameters:
+///
+/// * `FixedArray` : The FixedArray to check.
+///
+/// Returns `true` if the FixedArray has no elements, `false` otherwise.
+///
+/// Example:
+///
+/// ```moonbit
+/// test "FixedArray::is_empty" {
+///   let empty : FixedArray[Int] = []
+///   inspect!(empty.is_empty(), content="true")
+///   let non_empty = [1, 2, 3]
+///   inspect!(non_empty.is_empty(), content="false")
+/// }
+/// ```
+pub fn FixedArray::is_empty[T](self : FixedArray[T]) -> Bool {
+  self.length() == 0
+}

builtin/fixedarray_test.mbt

@@ -31,3 +31,8 @@ test "compare" {
   inspect!(arr3.compare(arr1), content="-1")
   inspect!(arr1.compare(arr1), content="0")
 }
+
+test "is_empty" {
+  let arr : FixedArray[Int] = []
+  assert_true!(arr.is_empty())
+}