Method contains

extern/boost/boost/function/function_base.hpp:659–667

  template<typename F>
    bool contains(const F& f) const
    {
      if (const F* fp = this->template target<F>())
      {
        return function_equal(*fp, f);
      } else {
        return false;
      }
    }

#if defined(__GNUC__) && __GNUC__ == 3 && __GNUC_MINOR__ <= 3
  // GCC 3.3 and newer cannot copy with the global operator==, due to