> The C++ inline keyword is treated similarly as well, with different metrics used of course.

You are thinking of C's inline/static inline.

C++'s "inline" semantics (which are implied for constexpr functions, in-class-defined methods, and static constexpr class attributes) allow for multiple "weak" copies of a function or variable to exist with external linkage. Rather than just an optimization hint it's much more of a "I don't want to put this in any specific TU" these days.