How to declare a compile-time constant scope to a class within a local scope

I have a class defined within a function. An object of that class type is instantiated later in the function, and I want to define a constant inside that class, which is referred to from the function.

Live code

void foo() {      class Internal {      public:          // here is the constant !!!          static constexpr int NONE = std::numeric_limits<int>::max();          // ------------------------          Internal(int n = NONE) : _n(n) {}          int get() const { return _n; }      private:          int _n;      };            Internal x(123), y;            if (x.get() == Internal::NONE) {         std::cout << "x" << std::endl; // not printed      }      if (y.get() == Internal::NONE) {         std::cout << "y" << std::endl; // printed      }  }  

This yields a compile error:

error: local class 'class foo()::Internal' shall not have static data member 'constexpr const int foo()::Internal::NONE' [-fpermissive]

Removing the static, leaving just constexpr, results in:

error: non-static data member 'NONE' declared 'constexpr'

Just using const results in:

error: invalid use of non-static data member 'foo()::Internal::NONE'

FWIW, static const doesn't work either.

Is there any way to accomplish this aside from moving the constant out of the class scope?

https://stackoverflow.com/questions/66501709/how-to-declare-a-compile-time-constant-scope-to-a-class-within-a-local-scope March 06, 2021 at 10:08AM