Defenition of small function to declare it as inline

Question

I saw a lot of posts about declaring methods as inline.
One of the rule of thumb to use inline is when the method is very small.
I guess there is no specific number for it - but how small is very small?
1 line (for example - Getter/Setter)?
~10/100 lines?

Answer 1

I have a 20 line template function which uses many constants (for the logic to be clear).

I could write it as a 1 liner, but it would not be understandable as easily.

When compiled with optimization the function can sometimes be just 1 assembler instruction. So it is marked for inline.

So lines of code is not a good measure.

inline is just a hint for the compiler. It doesn't have to inline. And even when there is no inline the compiler can do it.

I do research before applying inline, as there can be negative consequences (code slowing down due to bloat).

So as usual, measure if it improves your code.