Lambdas and classes

So far, we have learned how to write lambdas in C++. All the examples use lambda expressions outside classes, either as variables or as part of the main() function. However, most of our C++ code lives in classes. This begs the question—how can we use lambdas in classes?

To explore this question, we need an example of a simple class. Let's use a class that represents basic imaginary numbers:

class ImaginaryNumber{
    private:
        int real;
        int imaginary;

    public:
        ImaginaryNumber() : real(0), imaginary(0){};
        ImaginaryNumber(int real, int imaginary) : real(real), 
        imaginary(imaginary){};
};

We want to use our new-found lambda superpowers to write a simple toString function, as shown in the following code:

string toString(){
    return to_string(real) + " + " + to_string(imaginary) + "i";
}

So, what...