gistfile1.cpp

template <class F>
struct Fixed {
    F f;
    template <class... Args>
    decltype(auto) operator()(Args&&... args) const {
        return f(std::ref(*this), std::forward<Args>(args)...);
    }
};

template < class F >
Fixed(F) -> Fixed<F>;

gistfile2.cpp

Fixed fib17 = {
    [](auto f, int n) -> int
    {
        switch ( n ) {
            case 0: return 0;
            case 1: return 1;
            default: return f( n - 2 ) + f( n - 1 );
        }
    }
};

gistfile3.cpp

auto fib17 = Fixed
{
    [](auto f, int n) -> int
    {
        switch ( n ) {
            case 0: return 0;
            case 1: return 1;
            default: return f( n - 2 ) + f( n - 1 );
        }
    }
};