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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?
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The class template std::variant represents a type-safe union. An instance of std::variant at any given time either holds a value of one of its alternative types, or in the case of error - no value (this state is hard to achieve, see valueless_by_exception).
std::variant (C++17)An instance of std::variant has a value from one of its types. The value must not be a reference, C-array or void. A std::variant can have one type more than once. A default-initialized std::variant will be initialized with its first type.
To print a variant, enter its name on the initial screen of the variant maintenance tool, select either Attributes or Values in the sub-objects group box and choose Print. Note that you cannot print the values if you are working in change mode. The Print Screen List screen appears.
std::visit from C++17 is a powerful utility that allows you to call a function over a currently active type in std::variant . In this post, I'll show you how to leverage all capabilities of this handy function: the basics, applying on multiple variants, and passing additional parameters to the matching function.
This page says, that GCC 7 has std::variant.
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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.
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