Odd example of a template inheriting from its own specialization

template-inheriting-from-its-own-specialization.cc

#include <iostream>
#include <string>

// Template which inherits from its own specialization, as I first saw in
// https://stackoverflow.com/a/28213747/751579, which surprised me

template <typename T>
struct Foo : public Foo<decltype(T::x)> {
  T xxx;
};

template <typename TT>
struct Foo<TT*> {
  TT* p;
};

template <typename TT>
struct Foo<TT&> {
  TT r;
};

struct Has_x {
  std::string* x;
};

int main()
{
    std::string s{"I'm 's'"};
    Foo<Has_x> foo_has_x;
    foo_has_x.p = &s;

    std::cout << typeid(foo_has_x).name() << " - " << *foo_has_x.p << std::endl;
}