Re: '*' cannot appear in a constant-expression problem

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#include <string>
#include <map>
#include <iostream>

class Pizza {
public:
    virtual void get_price() = 0;
};
 
class HamAndMushroomPizza: public Pizza {
public:
    virtual void get_price() {
        std::cout << "Ham and Mushroom: $8.5" << std::endl;
    }

    static Pizza* create_pizza() {
        return new HamAndMushroomPizza;
    }
};
 
class DeluxePizza : public Pizza {
public:
    virtual void get_price() {
        std::cout << "Deluxe: $10.5" << std::endl;
    }

    static Pizza* create_pizza() {
        return new DeluxePizza;
    }
};
 
class SeafoodPizza : public Pizza {
public:
    virtual void get_price() {
        std::cout << "Seafood: $11.5" << std::endl;
    }

    static Pizza* create_pizza() {
        return new SeafoodPizza;
    }
};

typedef Pizza* (*pizza_creator_ptr)(void);

class PizzaFactory {
private:
    static std::map<std::string, pizza_creator_ptr> creators;

    void init() {
        PizzaFactory::creators["Deluxe"] = &DeluxePizza::create_pizza;
        PizzaFactory::creators["Ham and Mushroom"] = &HamAndMushroomPizza::create_pizza;
        PizzaFactory::creators["Seafood"] = &SeafoodPizza::create_pizza;
    }

public:
    static PizzaFactory* get_instance()
    {
        static PizzaFactory * instance = 0;
        if (!instance) {
            instance = new PizzaFactory;
            instance->init();
        }
        return instance;
    }

    Pizza* create_pizza(const std::string& type) {
        std::map<std::string, pizza_creator_ptr>::iterator it;
        if ((it = PizzaFactory::creators.find(type)) != creators.end())
            return (*(it->second))();
        else
            return 0;
    }
};

std::map<std::string, pizza_creator_ptr> PizzaFactory::creators;

//usage
int main() {
    PizzaFactory* factory = PizzaFactory::get_instance();
    Pizza *pizza = 0;

    if (pizza = factory->create_pizza("Default")) {
        pizza->get_price();
        delete pizza;
    }

    if (pizza = factory->create_pizza("Ham and Mushroom")) {
        pizza->get_price();
        delete pizza;
    }

    if (pizza = factory->create_pizza("Seafood")) {
        pizza->get_price();
        delete pizza;
    }

    return 0;
}
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