Kouhei Sutou created ARROW-486:
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Summary: [C++] arrow::io::MemoryMappedFile can't be casted to
arrow::io::FileInterface
Key: ARROW-486
URL: https://issues.apache.org/jira/browse/ARROW-486
Project: Apache Arrow
Issue Type: Bug
Components: C++
Affects Versions: 0.2.0
Environment: Linux
Reporter: Kouhei Sutou
arrow::io::ReadWriteFileInterface inheritances arrow::io::FileInterface
as diamond style via:
* ReadableFileInterface -> InputStream -> FileInterface
* WriteableFileInterface -> OutputStream -> FileInterface
If we have diamond inheritance, we can't cast subclasses of
arrow::io::ReadWriteFileInterface such as arrow::io::MemoryMappedFile to
arrow::io::FileInterface.
C++:
#include <arrow/io/file.h>
int
main(void)
{
std::shared_ptr<arrow::io::MemoryMappedFile> memory_mapped_file;
std::shared_ptr<arrow::io::FileInterface> file = memory_mapped_file;
return 0;
}
Build result:
a.cc: In function 'int main()':
a.cc:8:52: error: conversion from
'std::shared_ptr<arrow::io::MemoryMappedFile>' to non-scalar type
'std::shared_ptr<arrow::io::FileInterface>' requested
std::shared_ptr<arrow::io::FileInterface> file = memory_mapped_file;
^~~~~~~~~~~~~~~~~~
We can resolve it by using virtual inheritance.
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