weird compiler error using bind2nd(): “member function already defined or declared” instead of “reference to reference”

Question

I recently spent quite some time understanding the error message when calling func() in this piece of code:

int main()
{
    vector< vector&l         


        

Answer 1

This behavior is well-defined (every correct C++ compiler will fail to compile your code).

From the standard (N3376) section D.9.3 on class template binder2nd, these two defintions of operator() exist:

typename Fn::result_type
operator()(const typename Fn::first_argument_type& x) const;

typename Fn::result_type
operator()(typename Fn::first_argument_type& x) const;

If first_argument_type is already a const T&, then they will be conflicting.

Answer 2

This isn't an answer, but I just want to record the modern C++11 solution, where all the small bind helpers are deprecated in favour of the universal std::bind:

#include <functional>
#include <vector>
#include <algorithm>

void func(std::vector<double> const & v, double * sum) { /* ... */ }

int main()
{
    std::vector<std::vector<double>> v;
    double sum = 0;
    std::for_each(v.begin(), v.end(), std::bind(func, std::placeholders::_1, &sum));
}

The variadic templates of C++11, as well as a more comprehensive collection of type-modifying traits, give std::bind much stronger deduction abilities than the previous components in <functional>.