Another composition

[fog]

class A has its children/derived classes B and C. class D is supposed to be
contained inside both B and C.

Is the code right for the above requirement?
class A
{
D d;
};

class B : public A;
class C : public A;

Now should all public and protected members in D be accessible to all
members of B and C?
Is this a good design?
Thanks for your help!

[Claudio Puviani]

Re: Another composition

"fog" <fog@turboweb.c om> wrote[color=blue]
> class A has its children/derived classes B and C. class D is supposed to be
> contained inside both B and C.
>
> Is the code right for the above requirement?
> class A
> {
> D d;
> };
>
> class B : public A;
> class C : public A;
>
> Now should all public and protected members in D be accessible to all
> members of B and C?
> Is this a good design?[/color]

Good design limits the visibility of the internals of a class as much as
possible, even to its descendents. Therefore, no, exposing the internals of A
would not be good design.

Claudio Puviani

[John Harrison]

Re: Another composition


"fog" <fog@turboweb.c om> wrote in message
news:LGohc.5548 $_o3.190274@bgt nsc05-news.ops.worldn et.att.net...[color=blue]
> class A has its children/derived classes B and C. class D is supposed to[/color]
be[color=blue]
> contained inside both B and C.
>
> Is the code right for the above requirement?
> class A
> {
> D d;
> };
>
> class B : public A;
> class C : public A;[/color]

Seems OK to me.
[color=blue]
>
> Now should all public and protected members in D be accessible to all
> members of B and C?[/color]

No they shouldn't. There's no inheritance of B from D or of C from D, so
there is no automatic access to D's members from B or C.
[color=blue]
> Is this a good design?[/color]

That depends entirely on what you are trying to do. Good design doesn't
exist in the abstract.

john

[velthuijsen]

Re: Another composition

> class A has its children/derived classes B and C. class D is supposed to be[color=blue]
> contained inside both B and C.
>
> Is the code right for the above requirement?
> class A
> {
> D d;
> };
>
> class B : public A;
> class C : public A;
>
> Now should all public and protected members in D be accessible to all
> members of B and C?
> Is this a good design?
> Thanks for your help![/color]

Seeing that d is declared in the private block of A neither B nor C
has access to it.