Question

我正在尝试为两个类Circle实现工厂，Square都继承自Shape。

class Shape {
public: 
    virtual static
    Shape * getInstance() = 0;

};

class Circle : public Shape {        
public:
    static const std::string type;

    Shape * getInstance() {
        return new Circle;
    }
};
const std::string Circle::type = "Circle";

class Square : public Shape {        
public:
    static const std::string type;

    Shape * getInstance() {
        return new Square;
    }
};
const std::string Square::type = "Square";

我现在想创建一个带有键作为形状类型（字符串）的映射，并将值作为指向相应派生类的getInstance（）的函数指针。有可能吗？

谢谢，基兰

Answer 1

好的，我弄错了。

1）不应该声明 - virtual static Shape * getInstance（）= 0; - 在Shape类中。

2）getInstance（）在所有其他类中应该是静态的。

这是完整的实施

class Shape {
public:

    virtual
    std::string getType() = 0;

};

class Circle : public Shape {

public:
static const std::string type;
    Circle() {

    }

    std::string getType() {
        return type;
    }

    static
    Shape * getInstance() {
        return new Circle;
    }
};
const std::string Circle::type = "Circle";

class Square : public Shape {

public:
static const std::string type;
    Square() {
    }

    std::string getType() {
        return type;
    }

    static
    Shape * getInstance() {
        return new Square;
    }
};
const std::string Square::type = "Square";

class Triangle : public Shape {

public:
static const std::string type;
    Triangle() {
    }

    std::string getType() {
        return type;
    }

    static
    Shape * getInstance() {
        return new Triangle;
    }
};
const std::string Triangle::type = "Triangle";


typedef Shape * (*getShape)();
typedef std::map<std::string, getShape > factoryMap;

class ShapeFactory {
public:
    static factoryMap shapes;
    Shape * getInstance(const std::string & type){
        factoryMap::iterator itr = shapes.find(type);
        if (itr != shapes.end()){
            return (*itr->second)();
        }
        return NULL;
    }

};

factoryMap ShapeFactory::shapes;

class ShapeFactoryInitializer {
    static ShapeFactoryInitializer si;
public:

    ShapeFactoryInitializer() {
        ShapeFactory::shapes[Circle::type] = &Circle::getInstance;
        ShapeFactory::shapes[Square::type] = &Square::getInstance;
        ShapeFactory::shapes[Triangle::type] = &Triangle::getInstance;
    }

};

ShapeFactoryInitializer ShapeFactoryInitializer::si;

Answer 2

虽然与您的问题没有多大关系，但如果您对现代C ++设计（工厂，智能指针等）感兴趣，您可以查看这本书：

http://www.amazon.co.uk/Modern-Design-Applied-Generic-Patterns/dp/0201704315/ref=sr_1_20?s=books&ie=UTF8&qid=1293359949&sr=1-20

谈论工厂，如何设计工厂等等。

PS：我不是这本书的作者，也没有给我任何回复的答案： - ）

Answer 3

将代码的最后一行更改为ShapeFactoryInitializer ShapeFactoryInitializer::si;，然后它将通过编译。

在map中存储派生类的成员函数指针

3 个答案: