c++ - C++中如何实现工厂设计模式？

Question

为了学习C++中的OOP，我想用工厂设计模式创建一个ToolFactory。

但我不知道我必须如何开发它。但我曾尝试开发它，但它不起作用。

您可以在下面找到我为创建 ToolFactory 编写的所有代码，这些代码可以创建带有 vector 的工具箱。

我希望我的问题能说清楚。

类:

勤杂工.hpp :

#ifndef BRICOLEUR_HPP
#define BRICOLEUR_HPP

#include <ScrewDriver.hpp>
#include <Saw.hpp>
#include <Hammer.hpp>
#include <string>

class Handyman
{
    public:
        void screw(ScrewDriver t){t.screw();}
        void cut(Saw s){s.cut();}
        void crack(Hammer m){m.crack();}
};

#endif

锤子.hpp :

#ifndef MARTEAU_HPP
#define MARTEAU_HPP

#include <iostream>
#include <Tool.hpp>
#include <ToolBreak.hpp>

class Hammer : public Tool, ToolBreak
{
    std::string nom;

    public:
        Hammer(std::string const & nom){this->nom = nom;}
        std::string get_nom(){return this->nom;}
        void crack(){std::cout << "Hammer crack" << std::endl;}
        ~Hammer();
};

#endif

锯.hpp :

....
#include <ToolCutting.hpp>

class Saw : public Tool, ToolCutting
{
    ....
    public:
        ....
        void cut(){std::cout << "Saw cut" << std::endl;}
        ....
};

#endif

Screwdriver .hpp :

....
#include <ToolScrewing.hpp>

class ScrewDriver : public Tool, ToolScrewing
{
    ....
    public:
        ....
        void screw(){std::cout << "ScrewDriver screw" << std::endl;}
        ....
};

#endif

界面

工具断点.hpp

#ifndef TOOLBREAK_HPP
#define TOOLBREAK_HPP

#include <string>

class ToolBreak
{
    public:
        virtual std::string get_nom() = 0;
        virtual void crack() = 0;
};

#endif

界面相同模型:

• 刀具切割.hpp
• 工具螺丝.hpp

工厂

工具工厂.hpp

#ifndef TOOLFACTORY_HPP
#define TOOLFACTORY_HPP

#include <memory>
#include <Tool.hpp>
#include <ScrewDriver.hpp>
#include <Hammer.hpp>
#include <Saw.hpp>

class ToolFactory
{
    public:
        static Tool create (std::string name, std::string arg);
};

#endif

工具工厂.cpp

#include <ToolFactory.hpp>

Tool ToolFactory::create(std::string name, std::string args)
{
    if(name.compare("Screwdriver") == 0)
    {
        return ScrewDriver(args);
    }
    else if(name.compare("Hammer") == 0)
    {
        return Hammer(args);
    }
    else if(name.compare("Saw") == 0)
    {
        return Saw(args);
    }
    else
    {
        std::cout << "Error ! Tool not found" << std::endl;
    }
}

main.cpp

#include <vector>
#include <Handyman.hpp>
#include <ToolFactory.hpp>

using namespace std;

int main()
{
    Handyman handy;
    ScrewDriver screwdriver("Blue screwdriver");
    Saw saw("Green saw");
    Hammer hammer("Yellow hammer");

    handy.screw(screwdriver);
    handy.cut(saw);
    handy.crack(hammer);

    Tool screwdriverV2 = ToolFactory::create("Screwdriver", "Screwdriver v2");

    screwdriverV2.display();
    return 0;
}

输出

clang++ -Wall -std=c++14 -c -o obj/main.o src/main.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/Handyman.o src/Handyman.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/Saw.o src/Saw.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/ScrewDriver.o src/ScrewDriver.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/Hammer.o src/Hammer.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/Tool.o src/Tool.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/ToolScrewing.o src/ToolScrewing.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/ToolBreak.o src/ToolBreak.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/ToolCutting.o src/ToolCutting.cpp -I include
clang++ -Wall -std=c++14 -c -o obj/ToolFactory.o src/ToolFactory.cpp -I include
src/ToolFactory.cpp:21:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
clang++ -Wall -std=c++14 -o bin/main obj/main.o obj/Handyman.o obj/Saw.o obj/ScrewDriver.o obj/Hammer.o obj/Tool.o obj/ToolScrewing.o obj/ToolBreak.o obj/ToolCutting.o obj/ToolFactory.o
./bin/main
ScrewDriver screw
Saw cut
Hammer crack
It's a tool

Answer 1

要保持对象类型，您需要通过指针而不是值来传递它，否则您将遇到对象切片问题。当您在创建时传递对象所有权时，您应该使用智能指针:

class ToolFactory
{
    public:
        static std::unique_ptr<Tool> create (std::string name, std::string arg);
};

std::unique_ptr<Tool> ToolFactory::create(std::string name, std::string args)
{
    if(name.compare("Screwdriver") == 0)
    {
        return std::make_unique<ScrewDriver>(args);
    }
    // note as your if has return statement you do not really need else
    ...
}

下一步可能是用 std::unordered_map 消除级联 if:

class ToolFactory
{
        using Creator  = std::function<std::unique_ptr<Tool>(std::string)>
        using Creators = std::unordered_map<std::string,Creator>;

        Creators m_creators;
    public:
        ToolFactory();
        std::unique_ptr<Tool> create (std::string name, std::string arg);
};

ToolFactory::ToolFactory()
{
     m_creators[ "Screwdriver" ] = []( std::string arg ) { return std::make_unique<ScrewDriver>(arg); }
     ...
}

std::unique_ptr<Tool> ToolFactory::create (std::string name, std::string arg)
{
    auto f = m_creators.find( name );
    if( f == m_creators.end() ) 
       throw std::runtime_error( "unknown type:" + name );
    return f->second( arg );
}

这样它不仅会更通用，而且您可以轻松地扩展它以动态添加新类型。