C++博客-子弹的VISIONS-随笔分类-1.2 闲人杂语

[设计模式] 上班路上突然想到的builder模式

子弹 — Fri, 08 Aug 2008 01:45:00 GMT

Only some thinking to help to think about the Builder Pattern, but it's not so intuitive.
Suppose that we want to save data to files.

class File { /*abstract file*/ };
class FileBuilder
{
public:
    virtual bool buildFileHeader() =0;
    virtual bool buildFileBody()   =0;
    virtual bool buildFileTail()   =0;
    virtual File* getFile()        =0;
};

class BmpFile : public File { .... };
class GifFile  : public File { .... };
class JpegFile : public File { .... };
//other kinds of files

class BmpFileBuilder : public FileBuilder
{
};

class GifFileBuilder : public FileBuilder
{
};

class JpegFileBuilder : public FileBuilder
{
};
//builders above implement those interfaces from FileBuilder
//other kinds of file builders

//usage
File* buildFile(FileBuilder* fb)
{
    fb.buildFileHeader();
    fb.buildFileBody();
    fb.buildFileTail();
    return fb.GetFile();
}
void func()
{
    FileBuilder* fb = new SomeFileBuilder();
    File* f = buildFile(fb);
    //use f
    ....
}

Key Points:
1. Each builder is responsible for its buildXXX()
2. Each builder builds one kind of File
3. the File would be created in builder's constructor

子弹 2008-08-08 09:45 发表评论

[设计模式] Understand Design Patterns -- Factory Method

子弹 — Thu, 17 Jul 2008 04:43:00 GMT

Factory Method

// interface
class People
{
public:
virtual void doWhat() =0;
virtual string type() const =0;
};

class Male : public People
{
public:
    virtual void doWhat();
    virtual string type() const;
    static People* creator();
};

class Female : public People
{
public:
    virtual void doWhat();
    virtual string type() const;
    static People* creator();
};

// interface
typedef People* (*CreateFcn)();
class PeopleFactory
{
public:
static People* producePeople(const string& type);
static addCreateFcn(const string& type, CreateFcn creator);

private:
static map createFcns;
};

People* PeopleFactory::producePeople(const string& type)
{
    //***1
    CreateFcn creator= createFcns[type];
    return creator();
}

---- test ----
void f()
{
    //***2
    const string t("Male"); //or "Female"
    People* p = PeopleFactory::producePeople(t);
    p->doWhat();
    delete p;
}

---- extension ----
class Hemophrodite : public People
{
    virtual void doWhat();
    virtual string type() const;
    static People* creator();
};

void g()
{
    //***3
    const string newType = "Hemophrodite";
    PeopleFactory::addCreateFcn(newType, Hemophrodite::creator);

    // usage
    const string t("Hemophrodite");
    People* p = PeopleFactory::producePeople(t);
    p->doWhat();
    delete p;
}

Cool!! OCP!!

---------
Key point:

1. How does the Factory Method create the instance
of classes through their type names?
How could this method follow the OCP?

2. Where does the type name come from?
-- config file
-- registry
-- other method

3. About extension

----------
Interface classes:
People & PeopleFactory

enjoy it!!

子弹 2008-07-17 12:43 发表评论

[经验教训] 设计要点

子弹 — Fri, 04 Jul 2008 09:36:00 GMT

软件设计要点

Key point: 大局思想分层思想

设计，有很多方法。不管哪种方法，都需要对待设计的对象的深入的了解。

要有大局思想，不能管中窥豹，见木不见林。

设计时，不能过多考虑细节。如果陷在细节里，要及时中止和退出。

自上而下，层层细化是一种不错的方法。

可以借用一下图形学中的“分层次细节模型”。

不同的层次应该有不同的细节。

结构化有助于思路清晰化。树型结构是一种不错的选择。

每个阶段只做好那个阶段的事，其他的事一律不能做（尽管能做极好也不行）。

多和人讨论心中的想法。多注意别人的思路，与已比较，取长补短。

通常，对于问题，越讨论越清晰。

子弹 2008-07-04 17:36 发表评论