Can we make more components available in import libraries?

[frederick-vs-ja]

I found that there were mirrorings of basic_string, basic_string_view, and expected in print.cpp during implementing WG21-P2093R14 because the corresponding headers were non-core.

Would it be better to make some headers/classes "partially core" so that we can directly use them in import libraries?

[cpplearner]

IIUC that will be ABI-incompatible with code built with e.g. /MD /D_ITERATOR_DEBUG_LEVEL=1.

[StephanTLavavej]

Yep. Any machinery injected into the STL's import lib (for which we have only 2: release and debug) is effectively statically linked to the user's code. Therefore, such machinery cannot depend on _ITERATOR_DEBUG_LEVEL, which is why keeping basic_string out of the import lib is so critical. Core vs. non-core has been a reasonable way to enforce this restriction, and generally ensure that we keep complicated machinery out of the import lib. (For example, while basic_string_view doesn't have a varying representation, it has a lot going on, including _CONTAINER_DEBUG_LEVEL, and we'd prefer to avoid mix-and-match headaches with it.)