Re: The private-inheritance variant allows Car to override Engine's virtual functions

From:

werasm <werasm@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 29 Sep 2007 08:32:44 -0000

Message-ID:

<1191054764.151196.293790@50g2000hsm.googlegroups.com>

On Sep 29, 1:46 am, "Howard" <m...@here.com> wrote:

I find the comments above very confusing. (Does anyone else?)

How does private inheritance allow a class to expose its interface only to
specific clients?

See the example. Cmd exposes the function execute only to Processor.

What does "the same class at different levels" mean?
What's a "<bridge>"?

Refer to bridge pattern in wikipedia.

Perhaps some code example might illustrate your point(s) better. I'm just
not following.

Here goes:

struct Executable
{
    virtual void execute() = 0;
  protected:
    virtual ~Executable(){ }
};

struct Processor
{
  virtual void process( Executable& );
  //...
};

class Cmd : Executable
{
  public:
    Cmd( Processor* p = 0 ): p_( p ){ }
    void operator()()
    {
      if( p_ )
      {
        p_->process( *this );
      }
      else
      {
        execute();
      }
    }
  private:
    virtual void execute()
    {
      //...Some default behavior...
      // Most probably overridden
    }
    Processor* p_;
};

void clientFunction()
{
  Processor p;
  Cmd cmd( &p );
  cmd(); // Processor calls execute...
  cmd.execute();//Fails to compile...
}

Regards,

Werner