Why there is no concept of "const-correctness" for class's static member functions?

Question

Use case:

class A {
  static int s_common;
public:
  static int getCommon () const { s_common; };
};

Typically this results in an error as:

error: static member function ‘static int A::getCommon()’ cannot have cv-qualifier

This is because constness applies only to the object pointed by this, which is not present in a static member function.

However had it been allowed, the static member function's "const"ness could have been easily related to the static data members.
Why is this feature is not present in C++; any logical reason behind it ?

Answer 1

cv-qualifiers affect the function's signature. So you could have:

class A {
  static int s_common;
public:
  static void getCommon () const {  };
  static void getCommon () {  };
};

Now... how would you call the const one? There's no const object to call it on (well, you could call it on a const object, but that's not the point).

I'm just guessing here, there probably are other reasons. :)

Answer 2

However had it been allowed, the static member function's "const"ness could have been easily related to the static data members.

This is where your question becomes confused. A non-static member function declared as const still has non-const access to static data members. The const only applies to this (ie: the non-static data members).

It would make no sense for a static member function to use const in the same way syntactically, yet have a completely different outcome (ie: making access to static data members const).

Furthermore, static data members are nothing more than class-scoped global variables that have class access controls (public/private/etc) on them. So it doesn't make sense for some functions to have different const access to them, especially based on their signature.