Re: Newbie Modelling Interface Question

From: AdamJoe1 (adamjoe1_at_yahoo.co.uk)
Date: 10/27/03 

Date: Mon, 27 Oct 2003 22:40:19 -0000

Responding to H. S. Lahman,

Thanks for the reply.

> > One option I've considered is to have two interfaces. The first is
IMemory,
> > which Rom derives from and provides one pure virtual function, CrcCheck.
The
> > second is IRWMemory which Fram derives from and provides pv functions
Read,
> > Write, and CrcCheck. The client then has a pointer to each interface.
> >
> > Another option is to have two interfaces again but one derives from the
> > other. IRWMemory would derive from IMemory and inherit its CrcCheck
> > operation. Rom would derive from IMemory and Fram from IRWMemory. Again
the
> > client would have a pointer to each interface.
>
> Both these approaches expose the subsystem implementation, at least
> indirectly, to the clients. That should be avoided. If you need
> different interfaces for different client contexts, then subclass the
> Facade wrapper, not the individual class interfaces.

I'm not sure I understand this. How do these approaches expose the subsystem
implementation if the client only sees the interface? I thought the whole
point of an interface was to prevent exposing the implementation. What is it
I'm not getting?

My approach so far has not included the use of Facades. I guess this is
because most of my subsystems have relatively simple interfaces and I
haven't felt the need to use them. The classes that derive from these
interfaces are fairly simple too. Perhaps that was wrong. Are you saying
that I should use a Facade regardless of how simple the interface and its
implementation are? Or could it be that now with a more complex interface a
Facade is more appropriate?

[snip]

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