Mu (Type-level fixpoint combinator) in C++

woah.cpp

#include <vector>
#include <iostream>

template<template<typename Q> class T>
struct Mu {
  T<Mu<T> > In;
};

template<typename T>
struct Ptr {
  T* ptr;
};
char foo[] = "foo";

template<const char* P>
struct Foo {
  void f() { std::cout << P << std::endl; }
};

   
int main() {
Mu<Ptr> p;
Mu<std::vector> v;
Foo<foo> f; 
v.In.resize( 1 );
std::cout << v.In.size() << std::endl;
std::cout << v.In[0].In.size() << std::endl;
f.f();
return 0;
}