Design problem with Shared object loader.

Question

Hi, I have been developing this class for loading plugins in the form of shared objects for an application. I currently have thought of 2 ways of loading the file names of all the plugins to be loaded by the app. I have written an interface for loading file names. I have a few questions about how to improve this design. Please help. Thanks.

EDIT: Code change per feedback :D.

#include "Plugin.h"

//This class is an interface for loading the list of file names of shared objects. 
//Could be by loading all filienames in a dir, or by loading filenames specified in a file.
class FileNameLoader
{
    public:
        virtual std::list<std::string>& LoadFileNames() = 0;
};

class PluginLoader
{
public:
    explicit PluginLoader(LoadingMethod, const std::string& = "");
    virtual ~PluginLoader();

    virtual bool Load();

    virtual bool LoadPlugins(FileNameLoader&);
    virtual bool LoadFunctions();

protected:
private:
    explicit PluginLoader(const PluginLoader&);
    PluginLoader& operator=(const PluginLoader&);

    bool LoadSharedObjects();

    list<std::string> l_FileNames;
    list<PluginFunction*> l_Functions;
    list<Plugin*> l_Plugins;
};

Anything that seems ugly still? Thanks for the feedback anyway.

Answer 1

You created a fine interface, but then you don't use it. And you then store the file names in a private member l_FileNames.

I would change the PluginLoader constructor to accept a FileNameLoader reference and use that reference to load file names. This way you won't need the LoadingMethod in the PluginLoader class.

Write two classes that implement the FileNameLoader interface, one for each loading method.

edit:

class FileNameLoader
{
    public:
        //RVO will work right? :D
        virtual std::list<std::string>& LoadFileNames() = 0;
};

class FileNameLoaderByFile : public FileNameLoader
{
public:
    std::list<std::string>& LoadFileNames()
    {
        //  ...
    }

}

class FileNameLoaderByDirectory : public FileNameLoader
{
public:
    std::list<std::string>& LoadFileNames()
    {
        //  ...
    }

}



class PluginLoader
{
public:
    explicit PluginLoader(FileNameLoader& loader)
    {
    fileNames = loader.LoadFileNames()
    }

    virtual ~PluginLoader();

private:
    list<std::string> fileNames;
};

Answer 2

It looks to me like you have your functionality spread across the enum, FileNameLoader, and the PluginLoader classes.

My suggestion would be to make a PluginLoaderByFile class, and a PluginLoaderByDir class - possibly with one inheriting from another, or possibly with a common base class. This way you can define other subclasses including the necessary additional code, and keep it encapsulated, if necessary, down the track.

This also makes it easier to use e.g. the factory or builder patterns in future.

Answer 3

As for your statement of the current problem. U can use either

• vector for params or
• since u are using a string u can as well parse it using some delimiter (say " ", ",")

However I wouldn't let the params or method of loading be visible in the PluginLoader.

Instead would use a common/generic interface.