c++11 - C++ lambda - capture member variable

Question

I have a class that has function pointer to kernel function, that can change from outside.

class Bar 
{
   public:
     int i;
}

class Foo 
{
   public:
     std::function<double()> kernel;
     Bar bar;         
};

int main()
{

  Foo f;
  f.kernel = []() -> double { return i * i; }; //this is not working obviously

}

How can I achieve behaviour that is "presented", eg. read class variables inside lambda. I can bypass it by passing f inside and write f.bar.i, but that is not very nice solution.

Answer 1

In C++14 you can write it as,

f.kernel = [&i = f.bar.i]() -> double { return i * i; };

If you don't have C++14, you can alternatively create another variable,

int &i = f.bar.i;
f.kernel = [&i]() -> double { return i*i; };

Though there's nothing wrong with passing f and writing f.bar.i.