Re: console programm with alias design

Hi,

I try to design a program which has to run on console. There is only one
exe/binary and depend on the calling name argv[0] the different
tasks/commands should be performed as aliases. It's the technique by
busybox or linux lvm tools in C and avoids a bunch of different
binaries. Now I want to write those using C++ classes and boost.

Ok, now I'm in design considerations. I have problems with the API for
this purpose.

This class starts as base class of all commands to be implemented:
---8<---
    class CommandContext : public boost::noncopyable {
    public:
        virtual const std::string& name() const = 0;
    };
--->8----

This is a sample command:
---8<---
    namespace po = boost::program_options;

    class FooCommand : public CommandContext {
    public:
        FooCommand();

    public:
        const std::string& name() const;

    private:
        std::string m_name;
        po::options_description m_desc;
        po::variables_map m_vm;
    };

FooCommand::FooCommand()
    : m_name("foo"),
      m_desc("foo description")
{
    m_desc.add_options()
        ("include-path,I",
         po::value< vector<string> >()->composing(),
         "include path")
        ;
}

const std::string& FooCommand::name() const {
    return m_name;
}
--->8---

Similar another command's implementation:
---8<---
BarCommand::BarCommand()
    : m_name("bar"),
      m_desc("bar description")
{
    m_desc.add_options()
        ("compression", po::value<int>(), "set compression level")
        ;
}
--->8---

and the app class self with main():

---8<---
    namespace po = boost::program_options;
    namespace fs = boost::filesystem;

    class app : public boost::noncopyable {
    public:
        app(int argc, char **argv);
        int exec();

    private:
        void setupCmdOptions();
        void parse(int argc, char **argv);

    private:
        fs::path m_path;
        po::options_description m_desc;
        po::variables_map m_vm;
        bool m_start;
        bool m_alias;
};

int main(int argc, char **argv) {
    try {
        app a(argc, argv);
        return a.exec();
    }
    catch(std::exception& e) {
        cerr << e.what();
        return 1;
    }
    catch(...) {
        cerr << "unexpected exception";
        return 1;
    }
}

app::app(int argc, char **argv)
    : m_path(argv[0], fs::native),
      m_desc("Allowed options"),
      m_start( true ),
      m_alias( false )
{
    setupCmdOptions();
    parse(argc, argv);
}

/// Declare the supported options.
void app::setupCmdOptions() {
    m_desc.add_options()
        ("help", "produce help message")
        ("version,v", "print version string")
        ;
}

void app::parse(int argc, char **argv) {
    po::store(po::parse_command_line(argc, argv, m_desc), m_vm);
    po::notify(m_vm);

    if (m_vm.count("help")) {
        cout << "This is app v0.8.15.\n\n"
             << "Usage: " << m_path.leaf() << " [options]\n\n";
        cout << m_desc << "\n";
        m_start = false;
        return;
    }

    if (m_vm.count("version")) {
        cout << "app v0.8.15\n";
    }

}

int app::exec() {
    if ( m_start )
        cout << "Start app\n";

    return 0;
}

The command classes should register self at the app class, using the
specific command line options (added to app's options_description /
variables_map. Therefore an "app help" lists the common help message,
"app foo help" the help for foo command only.

I suffer from the design of all the classes APIs. Using boost isn't the
problem yet :-)

Any ideas, short samples, help here?