now the only TODOs in the ragged.array class are unimplemented linear…

… algebra functions

src/ragged/_spec_array_object.py

@@ -6,6 +6,7 @@
 
 from __future__ import annotations
 
+import copy as copy_lib
 import enum
 import numbers
 from collections.abc import Iterator
@@ -232,8 +233,8 @@ def __init__(
             else:
                 self._device = "cuda"
 
-        if copy is not None:
-            raise NotImplementedError("TODO 1")  # noqa: EM101
+        if copy and isinstance(self._impl, ak.Array):
+            self._impl = copy_lib.deepcopy(self._impl)
 
     def __str__(self) -> str:
         """
@@ -867,7 +868,8 @@ def __setitem__(
         https://data-apis.org/array-api/latest/API_specification/generated/array_api.array.__setitem__.html
         """
 
-        raise NotImplementedError("TODO 31")  # noqa: EM101
+        msg = "ragged.array is an immutable type; its values cannot be assigned to"
+        raise TypeError(msg)
 
     def __sub__(self, other: int | float | array, /) -> array:
         """
@@ -930,26 +932,42 @@ def to_device(self, device: Device, /, *, stream: None | int | Any = None) -> ar
                 main memory; if `"cuda"`, the array is backed by CuPy and
                 resides in CUDA global memory.
             stream: CuPy Stream object (https://docs.cupy.dev/en/stable/reference/generated/cupy.cuda.Stream.html)
-                for `device="cuda"`.
+                for `device="cuda"`. Ignored if output `device` is `"cpu"`. If
+                this argument is an integer, it is interpreted as the pointer
+                address of a `cudaStream_t` object.
 
         https://data-apis.org/array-api/latest/API_specification/generated/array_api.array.to_device.html
         """
 
+        if isinstance(stream, numbers.Integral):
+            cp = _import.cupy()
+            stream = cp.cuda.ExternalStream(stream)
+
+        if stream is not None:
+            t = type(stream)
+            if not t.__module__.startswith("cupy.") or t.__name__ != "Stream":
+                msg = f"stream object must be a cupy.cuda.Stream, not {stream!r}"
+                raise TypeError(msg)
+
         if isinstance(self._impl, ak.Array):
             if device != ak.backend(self._impl):
                 if stream is not None:
-                    raise NotImplementedError("TODO 124")  # noqa: EM101
-                impl = ak.to_backend(self._impl, device)
+                    with stream:
+                        impl = ak.to_backend(self._impl, device)
+                else:
+                    impl = ak.to_backend(self._impl, device)
             else:
                 impl = self._impl
 
         elif isinstance(self._impl, np.ndarray):
             # self._impl is a NumPy 0-dimensional array
             if device == "cuda":
-                if stream is not None:
-                    raise NotImplementedError("TODO 125")  # noqa: EM101
                 cp = _import.cupy()
-                impl = cp.array(self._impl)
+                if stream is not None:
+                    with stream:
+                        impl = cp.array(self._impl)
+                else:
+                    impl = cp.array(self._impl)
             else:
                 impl = self._impl