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https://issues.apache.org/jira/browse/ARROW-3662?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16669966#comment-16669966
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Dimitri Vorona commented on ARROW-3662:
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> The idea of "const" files is a bit murky in itself :)
True in general. I'm not completely sure if mmap'ed files are different enough
to make an exception, but at least from the technical PoW you could get their
size as a const operation. Thinking about it, the Read(int,
shared_ptr<Buffer>*) method could also have a const version.
It came up when I tried to pass a const MemoryMappedFile& to a function. Surely
I can just pass a pointer, but it feels strange to do it for a read-only file,
especially when there isn't any seeking involved.
> [C++] Add a const overload to MemoryMappedFile::GetSize
> -------------------------------------------------------
>
> Key: ARROW-3662
> URL: https://issues.apache.org/jira/browse/ARROW-3662
> Project: Apache Arrow
> Issue Type: New Feature
> Affects Versions: 0.11.1
> Reporter: Dimitri Vorona
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
>
> While GetSize in general is not a const function, it can be on a
> MemoryMappedFile. I propose to add a const override directly to the
> MemoryMappedFile.
> Alternatively we could add a const version on the RandomAccessFile level
> which would fail, if a const size getting (e.g. without a seek) isn't
> possible, but it seems to me to be a potential source of hard-to-debug bugs
> and spurious failures. At would at least require a careful analysis of the
> platform support of different size getting options.
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