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tcfhgj an hour ago

are you sure?

https://stackoverflow.com/questions/69444641/c17-stdvariant-...

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jasode 19 minutes ago | parent | next [-]

To add to sibling comment...

GCC 11 (2021) std::visit was slower than virtual dispatch.

GCC 12 (2022) optimized std::visit so it can be faster than virtual dispatch.

https://shubhankar-gambhir.github.io/posts/your-stdlib-imple...

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creata 42 minutes ago | parent | prev [-]

If you take the linked benchmark and use the latest compiler version, the std::variant version is faster. The annoying thing about std::variant (and with some other features of modern C++) is that it generates a bunch of code that the compiler has to optimize away.

	▲	vlovich123 24 minutes ago \| parent [-]
		Somehow and for some reason rust enums don’t have this problem and are far more ergonomic and easier to work with (not to mention compile times are amazing). I don’t know exactly why it’s better to have it as a first class language primitive and why the compiler has such a problem with std::visit, but clearly c++ meta programming slows down things in a super linear way such that the compiler has problems both from code gen and then optimization.