Why is it not possible to use private method in a lambda?

Question

Having a class like this:

class A {
public:
    bool hasGrandChild() const;

private:
    bool hasChild() const;
    vector children_;
};
         


        

Answer 1

You can capture this explicitly and make it a "member lambda" that has access to private members.

For example, consider the following sample:

#include 
class A {
private:
    void f() { std::cout << "Private"; }
public:
    void g() { 
        [this] { 
            f(); 
            // doesn't need qualification 
        }(); 
    }
};
class B {
private:
    void f() { std::cout << "Private"; }
public:
    void g() { [] { f(); }(); } // compiler error
};
int main() {
    A a;
    a.g();
}