cuda::barrier is default constructible for some reason, while cuda::std::barrier is not

[brycelelbach]

https://godbolt.org/z/Ka6GKb

http://eel.is/c++draft/thread.barrier.class

Neither should be default constructible.

[griwes]

It's default constructible so that you can put it into shared memory (including the future where there's dynamic init for that - unless you can refer to the block size variables in shared variable construction somehow?).