Can I create anonymous classes in C++ and capture the outside variables like in Java?

Question

In Java, when I need a callback function, I have to implement an anonymous class. Inside the anonymous class, I can access the outside variables if they\'re final

Answer 1

There is no way to automatically capture those variables, but you can use an alternative approach. This is if you want to capture by reference:

int main() {
    int y = 100; // mark y as final if possible
    class IB : public IA {
    public:
      IB(int& y) : _y(y) {}
      int f(int x) { return x + _y; }
    private:
      int& _y;
    } a (y);
    return 0;
}

If you want to capture by value, just change int& into int.

Anyway, you may consider using a tuple of lambdas as a "multi-callback" object if that is what bothers you about individual lambdas. You would still have everything packed in one object and capturing would be done for free.

Just as an example:

auto callbacks = make_tuple(
    [] (int x) { cout << x << endl; },
    [&] () { cout << y << endl; }, // y is captured by reference
    [=] (int x) { cout << x + y << endl; }, // y is captured by value
    // other lambdas here, if you want...
    );