Raffi Enficiaud wrote:

To this point, I thought that using accumulate would be cleaner: std::accumulate(m.begin(), m.end(), double(0), & _1->*&aa::second);

std::accumulate takes a binary function. It doesn't do s += f(*i) as you seem to think, it does s = f(s, *i). So you should probably pass _1 + &_2->*&aa::second to it.