C++ Coroutine Using Template

MyCoroutine.cpp

// Template-based Coroutine continuation idea by Ross Bencina <rossb@audiomulch.com> May 2014.
// see: https://groups.google.com/forum/#!topic/comp.lang.c++.moderated/ryhWI6cX3Ko

#include <iostream>

class MyCoroutine {
    typedef MyCoroutine this_t;
    typedef bool (this_t::*coroutine_fn_t) ();
    coroutine_fn_t next_;

    // This is a stackless co-routine. Any state that needs to be retained
    // across yeild points needs to be stored at class scope.
    // Coroutine state:
    int i;

#define BEGIN_COROUTINE switch (PC) { case 0:;
#define YEILD(result) { next_ = &this_t::coroutine_fn<__LINE__>; return (result); case __LINE__:; }
#define END_COROUTINE {next_ = &this_t::coroutine_fn<__LINE__>; case __LINE__:;} }
    
    template<int PC>
    bool coroutine_fn() {
        BEGIN_COROUTINE

        std::cout << "before loop" << std::endl;
        YEILD(true);

        for(i=0; i < 5; ++i ){
            std::cout << "in loop " << i << std::endl;
            YEILD(true);
        }

        std::cout << "after loop A" << std::endl;
        YEILD(true);
        std::cout << "after loop B" << std::endl;

        END_COROUTINE
        return false; // Will repeat this value after termination.
    }

public:
    MyCoroutine()
        : next_( &this_t::coroutine_fn<0> )
    {
    }

    bool step() // returns true while continuing
    {
        return (this->*next_)();
    }
};


int main(int argc, char* argv[])
{
    std::cout << "*** Coroutine ***" << std::endl;
    MyCoroutine coro;

    while (coro.step()) /* nothing */ ;

    std::cout << std::endl;
 
    return 0;
}

Very interesting implementation.

What license do you put it under?