class Consumer {
    public:
        virtual void consume(int data) = 0;
    };
 
    class A {
    public:
        A(Consumer& consumer) : consumer_(consumer) {}
        void process(int data) { consumer_.consume(data); }
    private:
        Consumer& consumer_;
    };
 
    class B : public Consumer {
    public:
        B() {}
        void consume(int data) { /* consume data */ }
    };
 
   int main() {
       B* b_ = new B();
       A a_ = A(*b_);
       a_.process(5);
       return 0;
   }
 

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