Re: [boost] Mother of all Variants

On 31. May 2019, at 01:50, Robert Ramey via Boost wrote:

On 5/30/19 4:17 PM, Gottlob Frege via Boost wrote:

...

I'm going to say *most* classes have a throwing move operators. Why? Because most classes have a custom copy constructor (because people don't follow Rule of Zero like they should), and thus most classes don't have *any* move operations. So all the move operations are actually copy operations, and most of those classes have a string or vector or whatever, and can throw on copy. Now, having said that, none of those classes actually throw in "real life", because they only throw when memory is completely exhausted, and have probably crashed already. And on some systems that oversubscribe allocation, they don't throw at all, they just crash. Thus most move operators, whether they exist or not, don't really throw.

This rather illustrates my point. As it stands now we've got std::variant, boost::variant and boost::variant2. And while we're at it don't for get std::optional, boost::optional, boost::outcome, std::expected? and ...?

I don't think there's an general expectation that any of these are going to interoperate - but they might by accident.

Peter followed the spec for std::variant, so boost::variant2 is a drop-in replacement for std::variant. I think one should not use boost::variant anymore in new projects anymore. So the choice is really between std::variant (you need a C++17 compiler) and boost::variant2 (a C++11 compiler is sufficient), which are interchangeable. Hans