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From w...@apache.org
Subject arrow git commit: ARROW-486: [C++] Use virtual inheritance for diamond inheritance
Date Sun, 15 Jan 2017 17:19:44 GMT
Repository: arrow
Updated Branches:
  refs/heads/master 47115aa3e -> a098fd04f


ARROW-486: [C++] Use virtual inheritance for diamond inheritance

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.

Author: Kouhei Sutou <kou@clear-code.com>

Closes #282 from kou/use-virtual-inheritance-for-diamond-inheritance and squashes the following
commits:

e9d3a0b [Kouhei Sutou] ARROW-486: [C++] Use virtual inheritance for diamond inheritance


Project: http://git-wip-us.apache.org/repos/asf/arrow/repo
Commit: http://git-wip-us.apache.org/repos/asf/arrow/commit/a098fd04
Tree: http://git-wip-us.apache.org/repos/asf/arrow/tree/a098fd04
Diff: http://git-wip-us.apache.org/repos/asf/arrow/diff/a098fd04

Branch: refs/heads/master
Commit: a098fd04fe229a9ce6f1f531c54c0c9a8eed56c4
Parents: 47115aa
Author: Kouhei Sutou <kou@clear-code.com>
Authored: Sun Jan 15 12:19:37 2017 -0500
Committer: Wes McKinney <wes.mckinney@twosigma.com>
Committed: Sun Jan 15 12:19:37 2017 -0500

----------------------------------------------------------------------
 cpp/src/arrow/io/interfaces.h    | 4 ++--
 cpp/src/arrow/io/io-file-test.cc | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/arrow/blob/a098fd04/cpp/src/arrow/io/interfaces.h
----------------------------------------------------------------------
diff --git a/cpp/src/arrow/io/interfaces.h b/cpp/src/arrow/io/interfaces.h
index 8fe2849..fdb3788 100644
--- a/cpp/src/arrow/io/interfaces.h
+++ b/cpp/src/arrow/io/interfaces.h
@@ -83,12 +83,12 @@ class Readable {
   virtual Status Read(int64_t nbytes, std::shared_ptr<Buffer>* out) = 0;
 };
 
-class OutputStream : public FileInterface, public Writeable {
+class OutputStream : virtual public FileInterface, public Writeable {
  protected:
   OutputStream() {}
 };
 
-class InputStream : public FileInterface, public Readable {
+class InputStream : virtual public FileInterface, public Readable {
  protected:
   InputStream() {}
 };

http://git-wip-us.apache.org/repos/asf/arrow/blob/a098fd04/cpp/src/arrow/io/io-file-test.cc
----------------------------------------------------------------------
diff --git a/cpp/src/arrow/io/io-file-test.cc b/cpp/src/arrow/io/io-file-test.cc
index 20cd047..f18f7b6 100644
--- a/cpp/src/arrow/io/io-file-test.cc
+++ b/cpp/src/arrow/io/io-file-test.cc
@@ -419,5 +419,10 @@ TEST_F(TestMemoryMappedFile, InvalidFile) {
       IOError, MemoryMappedFile::Open(non_existent_path, FileMode::READ, &result));
 }
 
+TEST_F(TestMemoryMappedFile, CastableToFileInterface) {
+  std::shared_ptr<MemoryMappedFile> memory_mapped_file;
+  std::shared_ptr<FileInterface> file = memory_mapped_file;
+}
+
 }  // namespace io
 }  // namespace arrow


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