[account42]

Compilation units are mainly about symbol visibility and as you already realized at the end of your comment don't have anything to do with inlining as far as the C++ standard is concerned. Neither does the inline keyword btw.

The linker doesn't inline anything, LTO/LTCG is about running (part of) the compile process at link time. But that's really no concern for the C++ code but an implementation detail of the toolchain - you could just as well not have a separate link step and instead have the compiler process all compilation units in one step.

[kwant_kiddo]

yes, LTO itself does not inline but from a user point of view it does, and that is exactly my point. If you are a beginner and you do not come from C, then you might not think about these things (maybe you do I did not).

I get that it is just an implementation detail, but so are many things in C++ and you usually care about these things otherwise you would not be using the language in the first place.

Many projects also disable exceptions that is also an 'implementation detail' (or at least something that is definitely not required by the standard I would imagine), but now you are technically not writing C++ anymore.

I guess this is also one important thing when learning C++. The community is very fragmented, and there seems to be disconnect between C++ users and committee.