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https://issues.apache.org/jira/browse/ARROW-486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17657520#comment-17657520
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Rok Mihevc commented on ARROW-486:
----------------------------------
This issue has been migrated to [issue
#16129|https://github.com/apache/arrow/issues/16129] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [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
> Assignee: Kouhei Sutou
> Priority: Major
> Fix For: 0.2.0
>
>
> 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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