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我想知道如何实现以下设计。我没有努力遵循标准约定以将这个虚拟代码保持在最低限度（例如，包括警卫）。为了论证，我使用的是 C++03，并且只使用标准库组件。

TL;DR：我Restaurant和Recipe类之间存在循环依赖关系。我有std::set<>一个指向类中对象的指针，Recipe反之亦然Restaurant。我不能#include在另一个，但由于前向声明，编译器不允许我为集合声明自定义比较器，因为此时value_types 仍然是不完整的类型。有没有办法做到这一点？

我在代码中包含了更详细地解释我的问题的注释。

/*
 * restaurant.h
 */
#include <string>
#include <set>
/*
 * I cannot do this as recipe.h would need to include
 * restaurant.h, which restricts
 * me when I want to write a custom comparator.
 */
// #include "recipe.h"

class Recipe;

// I know this will not work as Recipe has not yet been declared.
struct RecipeComparator {
    bool operator() (const Recipe* lhs, const Recipe* rhs) { 
        return lhs->price() < rhs->price();
    }
};

class Restaurant {
    public:
        Restaurant(const std::string& name, float averagePrice);
        float averagePrice() { return m_averagePrice; }

    private:
        std::string m_name;
        float m_averagePrice;
        /*
         * I want to have the recipies sorted by their prices.
         * I cannot define RecipeComparator here as Restaurant
         * is an incomplete type till now. 
         */
        std::set< Recipe*, RecipeComparator > m_recipiesSorted;

        /*
         * This works, but does not do what I want.
         */
        std::set< Recipe* > m_recipies;
};

/*
 * recipe.h
 */
#include <string>
#include <set>
/*
 * I cannot do this as restaurant.h would need to include
 * recipe.h, so I need to forward declare, which restricts
 * me when I want to write a custom comparator.
 */
// #include "restaurant.h"

class Restaurant;

// I know this will not work as Restaurant has not yet been declared.
struct RestaurantComparator {
    bool operator() (const Restaurant* lhs, const Restaurant* rhs) { 
        return lhs->averagePrice() < rhs->averagePrice();
    }
};

class Recipe {
    public:
        Recipe(const std::string& name, float price);
        float price() { return m_price; }

    private:
        std::string m_name;
        float m_price;
        /*
         * This is what I want as I want to have the restaurants sorted
         * by their average prices.
         * I cannot define RestaurantComparator here as Restaurant
         * is an incomplete type till now. 
         */
        std::set< Restaurant*, RestaurantComparator > m_restaurantsSorted;

        /*
         * This works, but does not do what I want.
         */
        std::set< Restaurant* > m_restaurants;

};
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1 回答 1

4

一个想法是将您的 Comparator 定义移动到 .cpp 源，同时将声明保留在标头中。这样，restaurant.h仍然recipe.h只能通过名称相互引用，因此前向声明仍然足够。

// restaurant_recipe_comparators.h
// probably too long, give it a better name
struct RestaurantComparator
{
    bool operator() (const Restaurant *, const Restaurant *);
};

struct RecipeComparator
{
    bool operator() (const Recipe *, const Recipe *);
};

// restaurant_recipe_comparators.cpp
bool RestaurantComparator::operator() (const Restaurant* lhs, const Restaurant* rhs)
{ 
    return lhs->averagePrice() < rhs->averagePrice();
}


bool RecipeComparator::operator() (const Recipe* lhs, const Recipe* rhs)
{
    return lhs->price() < rhs->price();
}
于 2013-07-08T03:16:37.973 回答