How do I remove code duplication between similar const and non-const member functions?

Question

Let\'s say I have the following class X where I want to return access to an internal member:

class Z
{
    // details
};

class X
{
    std::vec         


        

Answer 1

Here's a C++17 version of the template static helper function, with and optional SFINAE test.

#include 

#define REQUIRES(...)         class = std::enable_if_t<(__VA_ARGS__)>
#define REQUIRES_CV_OF(A,B)   REQUIRES( std::is_same_v< std::remove_cv_t< A >, B > )

class Foobar {
private:
    int something;

    template
    static auto& _getSomething(FOOBAR& self, int index) {
        // big, non-trivial chunk of code...
        return self.something;
    }

public:
    auto& getSomething(int index)       { return _getSomething(*this, index); }
    auto& getSomething(int index) const { return _getSomething(*this, index); }
};

Full version: https://godbolt.org/z/mMK4r3