C++: concepts in C++ STL not available when running C++ on SoloLearn

Question

I tried running a program using the concept feature of C++20 on SoloLearn. It worked which means that SoloLearn is compiling the code using C++20.

But even though the code is compiling using C++20, the concepts in STL (like same_as, integral) are not available. See:
https://code.sololearn.com/cvK14aFiPsYD/?ref=app

It works here
http://coliru.stacked-crooked.com/a/685567040df7b2c7

The strange thing is that both SL and Coliru use GCC. So why can I use the STL concepts on Coliru but not on SoloLearn?

Answer 1

Yes, but the underlying functionality apparently has been in GCC for quite a while as a technical specification:

https://en.cppreference.com/w/cpp/experimental/constraints

Maybe that's why the keywords and syntax work, but not the header. It's a bit weird that not everything works, for example compound requirements nonetheless cause a compilation error. But other than that, I don't really have an explanation.

Answer 2

Actually, it seems SL does not compile with C++20:

https://code.sololearn.com/c18k2t3Mzvd5/?ref=app

This works on my local machine with GCC 10.2.0, and the same goes for many new headers like <bit>.

Answer 3

Shadow
But aren't concepts a feature of C++20? We can use concepts on SoloLearn.

Answer 4

Shadow
that makes sense. Thanks.

Answer 5

@Martin Taylor
You're right. I had thought that gcc was using C++20 because the 'concept' keyword and type constraints worked which are features of C++20.