Artem Pavlenko

ok with me /cc @joto @lightmare @springmeyer

@daminetreg - thanks for the PR! Using `mapbox::variant` with `boost::spirit` is what (at least partially) motivated me in the first place. So far I was adapting `mapbox::variant` to play nice...

@daminetreg - good point re:boost.karma, I recall now I ended up with rather verbose implementation to dispatch based on a stored type in variant : https://github.com/mapnik/mapnik/blob/master/include/mapnik/wkt/wkt_generator_grammar_impl.hpp#L59-L83

> What is the difference between mapnik::util::variant and mapbox::util::variant ? Is it a fork ? Nope, `mapnik::util::variant` inherits from `mapbox::util::variant` and adds `struct adapted_variant_tag` and `types` in order to work...

@springmeyer - is your analyser buggy ^ ?? I'm not getting warnings, maybe I'm missing something. ```clang-tidy --version LLVM (http://llvm.org/): LLVM version 5.0.0svn Optimized build. Default target: x86_64-apple-darwin16.7.0 Host CPU:...

```[ { "directory": "/Users/artem/Projects/mapbox/variant", "command": "/Users/artem/Projects/mapbox/variant/.toolchain/bin/clang++ -o out/bench-variant test/bench_variant.cpp -I./include -isystem test/include -s\ td=c++11 -Werror -Wall -Wextra -pedantic -Wformat=2 -Wsign-conversion -Wshadow -Wunused-parameter -O3 -DNDEBUG -march=native -DSINGLE_THREADED -fvisibility-inli\ nes-hidden -fvisibility=hidden -stdlib=libc++...

@kkaefer I'll take a look, thanks.

quick workaround : ```c++ struct alignas(1) Empty { std::uint8_t val = 1u; Empty() {}; }; ``` I'll see if [`is_empty`](https://en.cppreference.com/w/cpp/types/is_empty) can be used to add overloads for `empty` types.

@joto - do you have plans for `swap`? Should we steal `swap` from `std::variant` ?

@lightmare - I like the general idea around 'no_init`, thanks! Ideally would be nice not to require writing`no-op` code at all. I'll review in over coming days and maybe we'll...