Using std::variant in g++

Question

How can I use std::variant in g++? Why isn't there std::variant in std::experimental (though std::optional is)? What version of g++ do I need? I prefer not to use boost and I'd like to use standard library only.

Edit: it seems like only g++ 7 supports std::variant. Then my question is: when will it be released and what problems may I encounter when using its experimental version?

Ashjian

You should use the very latest version of g++ – Joy

@BasileStarynkevitch what is the version number? How can I get it? – Ashjian

Run g++ -v or g++ --version in a terminal – Joy

@BasileStarynkevitch I know my version number. I have g++-6.2 and g++-5.4. They do not have variant unfortunately – Ashjian

Answer 1

This page says, that GCC 7 has std::variant.

Fraktur

Yep, I see. How can I install it on Ubuntu? Or as I found out, GCC 7 has not been released yet, when will it be? – Ashjian

@AleksandrTukallo: Simply with download, configure; make; make install. Works perfect! – Fretwork

@Fretwork thanks! But what problems may I encounter when using it before release? Is it ok? – Ashjian

@AleksandrTukallo: It is in stage 3 which means that there are a number of open bugs which should be fixed in the next days. Maybe you run into one of them. But I believe that you even run faster in a unfixed bug of an older gcc version as in a new one from current pre release branch. Short answer: Give it a chance! You can have as many versions in parallel as you want. If it do not work: Write a bug report. It will help others! – Fretwork

Answer 2

GCC has an info page where you can check which language feature was implemented with which version. It looks like variant is not yet implemented.

Tumefaction

According to the table std::optional is also not implemented, though I can use it in my g++ 5.4: experimental optional. – Ashjian

There is always Boost.Variant – Nimbus

@Tumefaction Does the link list standard library status or only core language features? – Fraktur