On Mon, 8 Apr 2019 at 06:30, Robert Ramey via Boost <boost@lists.boost.org> wrote:
LOL - Looks good to me! So now we have std::variant that is guaranteed to have a valid state with no double buffer BS and no extra overhead.
I'll be curious to hear what otherothers have to say about this.
And here's the boost version as well: #include <type_traits> #include <variant> #include <boost/mp11.hpp> #include <boost/variant.hpp> namespace mp11 = boost::mp11; struct Foo { Foo ( ) = delete; }; template<typename... Args> struct safe_std_variant : public std::variant<Args...> { static_assert ( std::conjunction<std::is_trivially_constructible<Args>...>::value, "is not trivially constructible" ); }; template<typename... Args> struct safe_boost_variant : public boost::variant<Args...> { static_assert ( mp11::mp_all<std::is_trivially_constructible<Args>...>::value, "is not trivially constructible" ); }; int main ( ) { safe_std_variant<int, double, bool> sv1; // compiles safe_boost_variant<int, double, bool> sv2; // compiles safe_std_variant<int, double, bool, Foo> sv3; // does not compile safe_boost_variant<int, double, bool, Foo> sv4; // does not compile } degski -- *Microsoft, please kill Paint3D*