[SOLVED] Error C2679: binary '<<': no operator found which takes a right-hand operand of type 'main::<lambda_1>' (or there is no acceptable conversion)

Error C2679: binary '<<': no operator found which takes a right-hand operand of type 'main::<lambda_1>' (or there is no acceptable conversion)

I am learning to write lambda expression in cpp, Below is the code. I'm using Visual Studio 2022 on Windows.

#include<iostream>
using namespace std;

int main()
{
  int k = 98;
  int l = 23;

  auto lm_add = [k,l](int i, int j) {
    return i + j;
  };

  cout << "addition using lambda : " << "cool" << lm_add << endl;

  return 0;
}

I want to return the answer for given variables.

Solution

This

auto lm_add = [k,l](int i, int j) {
    return i + j;
};

Initializes lm_add with a lambda expression. Behind the scenes the compiler generates an unnamed unique type with a call operator with the specified signature, ie taking two integers, and with members for the captures (also two integers). That type has no << operator to pipe it to an outstream. It can be called:

std::cout << lm_add(k,l);

However, it captures k and l for no good reason. Perhaps you want to either capture the variables so you can call it without arguments:

auto lm_add = [k,l]() {
    return k + l;
};

std::cout << lm_add();

Or not capture them an pass the argumetns:

auto lm_add = [](int i,int j) {
    return i + j;
};

std::cout << lm_add(k,l);