What means “obey ODR” in case of inline and constexpr function?

Question

I just read that constexpr and inline functions obey one-definition rule, but they definition must be identical. So I try it:

inline void foo() {
    return;         


        

Answer 1

If you have:

file1.cpp:

inline void foo() { std::cout << "Came to foo in file1.cpp" << std::endl; }

and

file2.cpp:

inline void foo() { std::cout << "Came to foo in file2.cpp" << std::endl; }

and you link those files together in an executable, you are violating the one-definition-rule since the two versions of the inline function are not same.