Visitor pattern example

visitor-example.cpp

// https://en.wikipedia.org/wiki/Visitor_pattern
#include <iostream>
#include <memory>

class A;
class B;
class C;

struct Visitor
{
public:
    virtual void visit(A&) = 0;
    virtual void visit(B&) = 0;
    virtual void visit(C&) = 0;
    virtual ~Visitor();
};

struct Visitable
{
public:
    virtual void accept(Visitor&) = 0;
    virtual ~Visitable();
};

class A: public Visitable
{
public:
    void accept(Visitor& v) override;
};

class B: public Visitable
{
public:
    void accept(Visitor& v) override;
};

class C: public Visitable
{
public:
    void accept(Visitor& v) override;
};

class PrintVisitor: public Visitor
{
public:
    void visit(A&) override;
    void visit(B&) override;
    void visit(C&) override;
};

int main()
{
    std::unique_ptr<Visitable> data[] = {
        std::make_unique<A>(),
        std::make_unique<B>(),
        std::make_unique<C>()
    };
    PrintVisitor printer;
    for(auto& i: data){
        i->accept(printer);
    }
    return 0;
}

Visitable::~Visitable()
{
    ;
}

Visitor::~Visitor()
{

}

void PrintVisitor::visit(A &)
{
    std::cout << "operation for class A" << std::endl;
}

void PrintVisitor::visit(B &)
{
    std::cout << "operation for class B" << std::endl;
}

void PrintVisitor::visit(C &)
{
    std::cout << "operation for class C" << std::endl;
}

void A::accept(Visitor &v)
{
    v.visit(*this);
}

void B::accept(Visitor &v)
{
    v.visit(*this);
}

void C::accept(Visitor &v)
{
    v.visit(*this);
}