Specializing C++ template based on presence/absense of a class member?

Question

Consider the following:

struct A {
  typedef int foo;
};

struct B {};

template
struct C {};

I wa

Answer 1

Another (C++03) approach:

template
struct has_foo
{
private:
    typedef char no;
    struct yes { no m[2]; };

    static T* make();
    template
    static yes check(U*, typename U::foo* = 0);
    static no check(...);

public:
    static bool const value = sizeof(check(make())) == sizeof(yes);
};

struct A
{
    typedef int foo;
};

struct B { };

template::value>
struct C
{
    // T has foo
};

template
struct C
{
    // T has no foo
};