c – 以工厂模式传递值

我正在学习工厂设计模式.我无法弄清楚如何将参数传递给使用Factory模式创建的对象.

一个小傻的例子：

假设我有三个类,A类,B类和Class Number.数字是基类.此外,类A需要三个整数并具有添加它们的功能,而类B需要两个整数并添加它们

代码片段：

int main()
{

    Factory *facObj = new Factory();
    // Addition for Two Integers
    Number * numberObjOne = facObj->createObj("AddThreeInteger");
    Number * numberObjTwo = facObj->createObj("AddTwoInteger");
}

Factory.cpp

Number * Factory::createObj(string str)
{
    if (str == "AddThreeInteger")
    {
        return new A(1,2,3);
    }
    else if (str == "AddTwoInteger")
    {
        return new B(1,2);
    }
    else            
        return NULL;
}

问题：现在无论我做什么,我只能添加硬编码的数字.如何从客户端代码或main()传递这些整数值.这是一个愚蠢的例子,我是编程的新手.请帮助我.我怎么能不硬编码值并得到结果.我可以在facObj-> createObj传递值吗？我有意义吗？请帮助我.

解决方法:

完整,可运行的例子. c 11或更好.

注意使用unique_ptr.不要使用原始指针.

#include <iostream>
#include <memory>
#include <stdexcept>
#include <exception>
#include <utility>

template<class T, class...Args>
struct creatable_from {
    template<class X, class...Ys>
    static auto test(int) -> decltype(X(std::declval<Ys>()...), void(), std::true_type());

    template<class X, class...Ys>
    static auto test(...) -> decltype(std::false_type());

    static constexpr auto value = decltype(test<T, Args...>(0))::value;

};

struct Operation {
    virtual ~Operation() = default;

    virtual int operator()() const = 0;
};

struct Add : Operation
{
    Add(int x, int y)
    : x(x), y(y)
    {}

    int operator()() const override {
        return x + y;
    }

    int x, y;
};

struct Sub : Operation
{
    Sub(int x, int y)
    : x(x), y(y)
    {}

    int operator()() const override {
        return x - y;
    }

    int x, y;
};

struct AddSub : Operation
{
    AddSub(int x, int y, int z)
    : x(x), y(y), z(z)
    {}

    int operator()() const override {
        return x + y - z;
    }

    int x, y, z;
};

struct Factory
{
    template<class...Args>
    std::unique_ptr<Operation> create(const std::string& type, Args&&...args)
    {
        if (type == "Add") {
            return do_create<Add>(std::forward<Args>(args)...);
        }
        if (type == "Sub") {
            return do_create<Sub>(std::forward<Args>(args)...);
        }
        if (type == "AddSub") {
            return do_create<AddSub>(std::forward<Args>(args)...);
        }

        // default - return a null pointer, but would probably be better to
        // throw a logic_error
        return {};
    }

private:
    template<class T, class...Args>
    static auto do_create(Args&&...args)
    -> std::enable_if_t< creatable_from<T, Args...>::value, std::unique_ptr<T> >
    {
        return std::make_unique<T>(std::forward<Args>(args)...);
    }

    template<class T, class...Args>
    static auto do_create(Args&&...args)
    -> std::enable_if_t< not creatable_from<T, Args...>::value, std::unique_ptr<T> >
    {
        throw std::invalid_argument("wrong number of arguments");
    }

};

int main()
{

    auto facObj = Factory();
    auto t1 = facObj.create("Add", 2, 3);
    auto t2 = facObj.create("Sub", 3, 2);
    auto t3 = facObj.create("AddSub", 2, 3, 4);

    std::cout << (*t1)() << std::endl;
    std::cout << (*t2)() << std::endl;
    std::cout << (*t3)() << std::endl;
}

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标签：c,design-patterns,factory-pattern
来源： https://codeday.me/bug/20190829/1759164.html