Fix several warnings

[Martchus]

• Avoid implicit signedness conversions where possible
• Avoid c-style casts
• Avoid warnings about bypassing virtual dispatch in destructors

[aminya]

@ahupowerdns Could you take a look at this?

[aminya]

Instead of casting to void it is better to use [[maybe_unused]]

[aminya]

Suggested change

	void put(MDBRWTransaction& txn, const Class& t, uint32_t id, unsigned int flags=0)
	{
	(void)txn;
	(void)t;
	(void)id;
	(void)flags;
	}
	void put([[maybe_unused]] MDBRWTransaction& txn, [[maybe_unused]] const Class& t, [[maybe_unused]] uint32_t id, [[maybe_unused]] unsigned int flags=0)
	{}

[Martchus]

I suppose when making that PR I didn't want to raise the C++ standard to 17 but yes, [[maybe_unused]] would be generally preferable.

Note that this repository seems generally unmaintained so I wouldn't get my hopes up that this change is merged anytime soon. I personally just created a "custom" branch on my own fork (see https://github.com/Martchus/lmdb-safe). It is already 66 commits ahead of this one. I picked up some commits from pending PRs and did many adjustments myself. You might not want all changes from my branch but be sure to have a look.

[aminya]

Thanks! Maybe @ahupowerdns can add you as a maintainer so you can take over the project. It would be great to keep this effort going. Alternatively, we can create a new organization and put the code there.

[Martchus]

Maybe. Note that I've introduced a dependency to https://github.com/Martchus/cpp-utilities because I didn't want to C&P lots of build system code. That could be problematic for some users (although the library is not a runtime dependency, it is just used for CMake modules and a few headers). I've also introduced usage of https://github.com/Martchus/reflective-rapidjson but that's only optional (you can still use any serialization you want). Some of my changes might also be API breaks.