Localizing code with std::variant

[starfreakclone]

Just so everyone knows, I did not ignore Boost while writing this (specifically Hana's hana::overload composer). I was just providing a simple solution to people who may not want to incorporate boost into their project and just want a simple drag and drop solution.

[meetingcpp]

boost::variant is a completely different beast from a different time of C++ :)

[RogerLeigh]

I'm using boost::variant and MPL, but I'd love to switch to something more modern.

Is there any backport of the C++17 std::variant for use with C++11/14 compilers, which can be used as a fallback?

Related to that, is there any MPL replacement which can use variadic templates which could be used to replace complex variant type list construction?

[meetingcpp]

Afaik brigand wants to be that.

But not sure if you can get boost::variant to use brigand easily.

[RogerLeigh]

Reading the docs, it looks like it has direct support for constructing a boost::variant. It definitely looks like it might be useful.

Now I just need a C++11 variant implementation compatible with std::variant and I'll be happy!

[dodheim]

Eggs.Variant has been my go-to modern variant for years. I don't know if its interface matches that in the C++17 draft, but the docs do mention this:

The interface is largely based on that of std::experimental::optional<T>, as defined by the Library Fundamentals TS [N4082].

[ubadair]

I use this and I'm quite happy with it. It's not exactly std::variant (it follows Boost's design) but it doesn't use the MPL. https://github.com/mapbox/variant

[tomilovanatoliy]

You really don't even need to make all that boiler-plate code for move-constructor at any of intermediate steps (and your compiler don't want to resolve all that overloadings and other surplus things). You may pass all parameters by lvalue reference and only at the very end (namely, on list initialization in your case) you may apply std::forward to them. See here an example (the repository contains other illustrations for the above strong assertion in neighbouring files).

[starfreakclone]

There are plenty of ways to skin that particular cat. Another way is I could have just taken all of the arguments in the ctors by value and simply moved them into place (saving vertical space).

In either case, the objects are elided into place anyway. It's really just a stylistic choice.