C++ – The auto key word

A funny remark  which I discovered without realizing it ( Though I’m not the first one… ), is that the auto keyword can be used to access public members with private types, as so:

#include <iostream>
using namespace std;

class FooClass
{
private:
    struct PrivateFoo
    {
        bool m_bFoo;
    };

public:
    PrivateFoo m_Foo;
};

int main()
{
   FooClass foo;

   // The following code will produce an error,
   // you can't access the private type FooClass::PrivateFoo
   FooClass::PrivateFoo* fooPtr = &foo.m_Foo;

   // But this works
   auto fooPtrAuto = &foo.m_Foo;

   // Nothing fancy
   fooPtr->m_bFoo;
   fooPtrAuto->m_bFoo;

   return 0;
}

So as you know, I can’t use the type PrivateFoo directly, because it’s declared as private, but the auto keyword is permitted, even though it detects the type needed and, well, uses it. I see why is technically is permitted, but, logically, it doesn’t give any sense for me, though it might be usable.