alt Hacker News> There's an important behavioral difference between Scala 2 and 3: in 2, @inline was merely a suggestion to the compiler, whereas in 3, the compiler unconditionally applies the inline keyword. Consequently, directly replacing @inline with inline when migrating from 2 to 3 is a mistake.
This reminds me of a similar lesson C/C++ compilers had to learn with the "register" keyword. Early versions treated the keyword as a mandate. As compiler optimizers became more refined, "register" was first a recommendation and then ultimately ignored.
The C++ inline keyword is treated similarly as well, with different metrics used of course.
EDIT:
Corrected reference to early C/C++ keyword from "auto" to "register".
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And now we have things like `__attribute__((always_inline))` for GCC where you are completely, 100% sure that you want to inline :).
> 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.