This-pointer capture in lambda wrapper around recursive function

Question

I have a class template Wrap with a recursive member function test(int) that I want to pass to an STL algorithm with a lambda (std::

Answer 1

I believe this is a bug of GCC 4.7.2. The warning says:

missing initializer for member 'Wrap<T>::test2(int) [with T = int]::<lambda(int, const int&)>::__this'

Which means that the compiler recognizes the this pointer is to be captured and the generated closure does contain a pointer for it, but that pointer does not get initialized in the closure's constructor.

This is confirmed by the fact that attempting to access/change a member variable (which is not present in your example, but can be easily added) causes a run-time error. For instance, this shows no output at liveworkspace.org

#include <algorithm>
#include <iostream>
#include <vector>

template<typename T>
struct Wrap 
{
    int test2(int depth)
    {
        m_test++;
        std::vector<int> v = { 0, 1, 2, 3 };
        return depth == 0? 1 : std::accumulate(
             v.begin(), v.end(), int(0), [=](int sub, int const&) {
             return sub + /*this->*/test2(depth - 1);
             });   
    }

    int m_test = 0;
};

int main()
{
    Wrap<int> w;
    std::cout << w.test2(2) << "\n"; // 1
}

This code compiles fine with Clang 3.2 and VS2012, which seems to confirm the presence of a bug.