What's the best way to sum the result of a member function for all elements in a container?

Question

Let's say I have the following object:

struct Foo
{
    int size() { return 2; }
};

What's the best way (most maintainable, readable, etc.) to get the total size of all objects in a vector<Foo>? I'll post my solution but I'm interested in better ideas.

Update:

So far we have:

• std::accumulate and a functor
• std::accumulate and a lambda expression
• plain ol' for-loop

Are there any other workable solutions? Can you make something maintainable using boost::bind or std::bind1st/2nd?

Answer 1

In addition to your own suggestion, if your compiler supports C++0x lambda expressions, you can use this shorter version:

std::vector<Foo> vf;

// do something to populate vf


int totalSize = std::accumulate(vf.begin(),
                                vf.end(),
                                0, 
                                [](int sum, const Foo& elem){ return sum + elem.size();});