c++ - 如何强制实现者做某事

Question

假设我有以下类:

class X;
class Y;

class Collection
{
   public:
      virtual void AddItemX(X*) = 0;
      virtual void AddItemY(Y*) = 0;
      //So on...
};

class Collector
{
   public:
      virtual void Fill(Collection&) = 0;
};

有什么方法可以确保 Collector 类的实现将填充传递的 Collection 类中的所有需要​​的项目？

Answer 1

给定已知数量的 AddItemX() 调用的一种方法是将那些 AddItem() 函数移动到 protected 并让 Collection 类跟踪添加和数量，例如:

(我实际上不喜欢这个解决方案，大声笑，但考虑到您的设计就足够了:)

class X;
class Y;

class Collection
{
private:
    int m_nItems;
    int m_nItemsAdded;

protected:
    virtual void AddItemXImpl(X&) = 0;
    virtual void AddItemYImpl(Y&) = 0;

public:
    Collection() : m_nItems(2), m_nItemsAdded(0){};

    void AddItemX(X& _x) {m_nMethodsAdded++; AddItemXImpl(_x); };
    void AddItemY(Y& _y) {m_nMethodsAdded++; AddItemYImpl(_y); };

    // function to find out if we're filled
    bool isFilled() const {return(m_nItemsAdded == m_nItems); };
}; // eo class Collection

编辑:为澄清起见，您的收集器可以这样实现:

class Collector
{
protected:
    virtual void FillImpl(Collection& _collection) = 0;

public:
    void Fill(Collection& _collection)
    {
        FillImpl(_collection);
        if(!_collection.isFilled())
            throw(std::exception("Not filled dammit!"));
    };
}; // eo class Collector