avoid std::move() on temporary at -werror

[mattbenjamin]

/home/jenkins-build/build/workspace/ceph-pull-requests/src/rgw/driver/posix/lmdb-safe/lmdb-safe.cc:336:10: error: moving a temporary object prevents copy elision [-Werror,-Wpessimizing-move]
return std::move(getRWTransaction());
^
/home/jenkins-build/build/workspace/ceph-pull-requests/src/rgw/driver/posix/lmdb-safe/lmdb-safe.cc:336:10: note: remove std::move call here
return std::move(getRWTransaction());
^~~~~~~~~~ ~
1 error generated.

[Martchus]

This PR is likely in vain because this repository is no longer maintained.

I have fixed many more warnings on #15 which you may want to checkout. I have also done lots of further improvements on https://github.com/Martchus/lmdb-safe.

[mattbenjamin]

I saw that, and I'm going to try to use your repo, if you consider it maintained. If this change is still applicable, would you have accepted it?

[Martchus]

I would definitely have accepted it. Note l definitely still care about my fork repo as I actively use it in one of my projects. However, I have never spent the time to make it really fancy.

Note that LMDB in general needs a rediciously large address space which is likely a no-go on any 32-bit system. I'm just saying this as a warning so you know what you're getting into.

[mattbenjamin]

interesting; we're all 64-bit, so that should be ok :)

[mattbenjamin]

@Martchus so, is your lmdb-safe no longer standalone--it requires your c++utilities submodule to be present as well?

it seems like that is sort of accidentally true in global.h; would you consider a change to skip that inclusion if the client code defines LMDB_SAFE_STATIC? (since in that case, the code doesn't appear to use anything from c++utilities)

[Martchus]

It just uses headers and CMake modules from c++utilities but not the library itself. I suppose it would be ok to disable inclusion of c++utilities headers if e.g. LMDB_SAFE_NO_CPP_UTILITIES is defined. That would then disable all features that come with it, e.g. being able to export symbols in case one builds a shared library and the whole lmdb-typed.hh header as it really uses c++utilities headers.

Note that it shouldn't be hard to supply c++utilities as it provides a CMake module and pkg-config module. If you use CMake yourself you can also build it as part of your project (via add_subdirectory).

[mattbenjamin]

I only need the facilities in lmdb-safe.hh, and it's an advantage to avoid including as little extra as possible, in particular, a whole submodule. It's not about ease of building, it's about maintenance of our larger project.

[Martchus]

Ok, I would accept commit to switch off c++utilities in lmdb-safe.hh. By the way, have you considered using https://github.com/drycpp/lmdbxx? It seems more popular. I personally only opted for lmdb-safe because of lmdb-typed.hh.

[mattbenjamin]

well, I had seen it, but liked the interface work in lmdb-safe, liked it's style of c++. what is your opinion of lmdbxx?

[Martchus]

I haven't used lmdbxx myself yet. I would have chosen it if it would have had an interface similar to lmdb-typed.hh because it seems more popular and is more actively maintained.