Design Pattern --- Composite

qingwenclass Component
{
public:
    virtual void foo() = 0;
};
class LeafA : public Component
{
public:
    // Interface.
    virtual void foo() override { cout <<"LeafA::foo()." <<endl; }
};
class LeafB : public Component
{
public:
    // Interface.
    virtual void foo() override { cout <<"LeafB::foo()." <<endl; }
};
class Composite : public Component
{
    // data.
    vector<Component *> m_components;

public:
    // Interface.
    virtual void foo() override { for (auto i : m_components) { i->foo(); } }

    void add(Component *component) { m_components.push_back(component); }
};

int main(int argc, char *argv[])
{
    Composite *c1 = new Composite, *c2 = new Composite, *c = new Composite;
    c1->add(new LeafA);
    c2->add(new LeafA), c2->add(new LeafB);

    c->add(c1), c->add(c2);     // 这里体现了 Composite 模式的优势。 
                                // 不区别对待单个 Leaf 和 Composite。
                                // 使得递归每一个 Component 变得容易。

    c->foo();
    
    return 0;
}