Cant understand cpp snippet

Question

This snippet is lifted from bitcoin code base.

struct CombinerAll
{
    typedef bool result_type;

    template<typename I>
    bool operator()(I first, I last) const
    {
        while (first != last) {
            if (!(*first)) return false;
            ++first;
        }
        return true;
    }
};

This gets used here

boost::signals2::signal<bool (CNode*), CombinerAll> ProcessMessages;

I dont understand what it is for. Need help

Answer 1

From the function:

        if (!(*first)) return false;

If any of the elements in the range [first, last) evaluate to false when the pointer/iterator/object is dereferenced, the function returns false. Otherwise, it returns true.

Example test code:

int main()
{
   std::string sa = "abc";

   std::vector<int> va = {1, 1, 1};
   std::vector<int> vb = {1, 0, 2};

   std::cout << std::boolalpha;
   std::cout << CombinerAll()(sa.begin(), sa.end()) << std::endl;

   std::cout << CombinerAll()(va.begin(), va.end()) << std::endl;
   std::cout << CombinerAll()(vb.begin(), vb.end()) << std::endl;

   return 0;
}

Output:

true
true
false