#include <vector>
 
//Declare Original out so View can use its copy/move constructor
class Original
{
public:
    auto columns();
    const auto columns() const;
    std::vector<int> m;
};
 
//Full declaration/implementation of View
class View
{
public:
    View(const Original &that) : m(that) { }
    Original m;
};
 
//Now that View's constructors are defined, implement these Original funcs
auto Original::columns() {return View(*this);}
const auto Original::columns() const {return View(*this);} // comment #1
 
int main()
{
    Original o1;
    const Original o2;
    o2.columns(); // comment #2
}

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