There is no particular difficulty in having one-shot continuations in C (or C++) and in fact over the last few decades there have been plenty of libraries implementing them. They just never caught on with the general C and C++ programming population, although they were popular in some niches.
C with Classes had them from the beginning, as Stroustrup liked them in Simula, but then (like many other things) had to take them out of the language after user feedback.
Re stackless coroutines and language support, while it is relatively straightforward to have stackfull coroutines as a library, the stackless kind in practice needs to be implemented as a language feature.
C with Classes had them from the beginning, as Stroustrup liked them in Simula, but then (like many other things) had to take them out of the language after user feedback.
Re stackless coroutines and language support, while it is relatively straightforward to have stackfull coroutines as a library, the stackless kind in practice needs to be implemented as a language feature.