Improvements and fixes for C++ nullable implementation and reduce dynamic allocation

[glenfe]

Covers points 1, 2, 3, 4, and 6 that I raised in issue #167 as well as reduce two additional dynamic allocations.

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[glenfe]

The space saving is actually more than just 1 byte. That is, the empty base optimization there actually saves alignof(value_type) bytes in the case of the first specialization, and saves alignof(pointer) bytes in the case of the second specialization. e.g. This could be up to 8 bytes on 64-bit, or 4 bytes on 32-bit for certain nullable<T> types.

[chwarr]

I think it would be clearer if we used Allocator in these ctors, as that's the name of the base.

[glenfe]

Sure.

[chwarr]

Left some comments. Be sure to look at the comments on outdated diffs, because GitHub doesn't understand that reviewing individual commits is a thing. :-(

[glenfe]

The rationale for !!pointer over static_cast<bool>(pointer) is, of course, that MSVC and its diagnostics are, as ever, defective. (You should later consider disabling that warning like you do so many others in warning.h)

[jasonzio]

I'm not a big fan of disabling warnings. If you chose to do so, please wrap it tightly around the offending line of code; don't do it globally for the entire file or, worse yet, the entire project. Warnings really do help catch problems; a tightly-wrapped deviation (disable, then the offending line of code, then re-enable) shows the warning was investigated, determined to be benign, and silenced.

[glenfe]

I'm a big fan of disabling stupid warnings, especially globally. It shows a sensible intolerance to a defective C++ implementation.

[chwarr]

!!pointer seems like a good compromise.

[chwarr]

Confirmed size reduction of bond::nullable<std::string> a pointer size (8 bytes [56 to 48] with Visual Studio 14 2015 Win64 and 4 bytes [36 to 32] with Visual Studio 14 2015). 🎉

I'm going to run some x86 builds myself, as these aren't part of the CI builds.

[chwarr]

Bond version 4.3.0 is now live on NuGet.org. These changes are included in that version. You'll also need to pull down the latest C++ source code as well.