Avoid needless casting of masks

astropy/utils/masked/function_helpers.py

@@ -440,10 +440,27 @@ def sort_complex(a):
         return b
 
 
-@apply_to_both
-def concatenate(arrays, axis=0, out=None, **kwargs):
-    data, masks = _get_data_and_masks(*arrays)
-    return (data,), (masks,), dict(axis=axis, **kwargs), out
+if NUMPY_LT_1_20:
+    @apply_to_both
+    def concatenate(arrays, axis=0, out=None):
+        data, masks = _get_data_and_masks(*arrays)
+        return (data,), (masks,), dict(axis=axis), out
+
+else:
+    @dispatched_function
+    def concatenate(arrays, axis=0, out=None, dtype=None, casting='same_kind'):
+        data, masks = _get_data_and_masks(*arrays)
+        if out is None:
+            return (np.concatenate(data, axis=axis, dtype=dtype, casting=casting),
+                    np.concatenate(masks, axis=axis),
+                    None)
+        else:
+            from astropy.utils.masked import Masked
+            if not isinstance(out, Masked):
+                raise NotImplementedError
+            np.concatenate(masks, out=out.mask, axis=axis)
+            np.concatenate(data, out=out.unmasked, axis=axis, dtype=dtype, casting=casting)
+            return out
 
 
 @apply_to_both