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

Question

I am learning to write lamda expression in cpp, Below is the code Using visual studio 2022 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 lambada : " << "cool" << lm_add << endl;

  return 0;

Wanted to return the answer for given variables.

Answer 1

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);