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From "Kouhei Sutou (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ARROW-486) [C++] arrow::io::MemoryMappedFile can't be casted to arrow::io::FileInterface
Date Sun, 15 Jan 2017 06:49:26 GMT
Kouhei Sutou created ARROW-486:
----------------------------------

             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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