C function pointers with C++11 lambdas

Question

So i\'m trying to write an Integration function to be used with c++11 lambdas. The code looks something like this:

double Integrate(std::function

        

Answer 1

A std::function<> cannot be converted to a function pointer. std::function<> are function objects that can potentially hold state while regular functions are stateless (kind of, you could potentially have static variables, but that is a different thing).

On the other hand, stateless lambdas can be converted to a function pointer, so you could potentially change the signature of your function to take a function pointer directly and the lambda will be converted:

double Integrate(double(*func)(double,void*), double a, double b, 
                 std::vector & params) // !!!

std::vector p{2,3};
Integrate([](double a,void* param)
   {
      std::vector *p = static_cast*>param;
      return p->at(0)*a+p->at(1);
   }
   ,0,3,p);

Note that it is illegal to bind an rvalue to a non-const reference, so you cannot legally pass {2,3} as the last argument to Integrate (even if Visual Studio allows you to), you will need to create a named variable.