The receiver's write file handle.
- iOS 2.0+
- macOS 10.0+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
This object is automatically deallocated when the receiver is deallocated.
You use the returned file handle to write to the pipe using
write method. When you are finished writing data to this object, send it a
close message to delete the descriptor. Deleting the descriptor causes the reading process to receive an end-of-data signal (an empty