[C++] Support casting from storage type to extension type #30057
Description
We already support casting an extension array to its storage type (ARROW-7858):
>>> from pyarrow.tests.test_extension_type import IntegerType
>>> arr = pa.array([1, 2, 3], pa.int64())
>>> arr_ext = pa.ExtensionArray.from_storage(IntegerType(), arr)
>>> arr_ext.cast(arr.type)
Out[29]:
<pyarrow.lib.Int64Array object at 0x7f7b0d4739a0>
[
1,
2,
3
]but we don't support the cast the other way around from storage type to extension type:
>>> arr.cast(arr_ext.type)
...
ArrowNotImplementedError: Unsupported cast from int64 to extension<arrow.py_extension_type<IntegerType>> (no available cast function for target type)
../src/arrow/compute/cast.cc:119 GetCastFunctionInternal(cast_options->to_type, args[0].type().get())Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Miles Granger / @milesgranger
Related issues:
- [C++][Python] Support casting an Extension type to its storage type (is related to)
- [C++] Cast dictionary of extension type to extension type (is related to)
PRs and other links:
Note: This issue was originally created as ARROW-14500. Please see the migration documentation for further details.