Why full specialization of template function is not picked up from the .cpp file without declaration?

Question

Following code generate no compilation/linker error/warning:

// A.h
#include
struct A
{
  template
  static void foo (T t)
  {
         


        

Answer 1

All explicit specialization declarations must be visible at the time of the template instantiation. Since your explicit specialization declaration for A::foo is visible in one translation unit but not the other, the program is ill-formed.

(In practice, the compiler will instantiate the primary template in main.cpp and the explicitly-specialized one in other.cpp. That would still an ODR violation anyway.)