[Exceptional C++ Style] Item 14: Order, Order!

[Kevlin Henney]

In message 
<20041210091455.HFZU20377.aamta02-winn.mailhost.ntl.com@[62.253.162.95]>,
  Ric Parkin <ric.parkin at ntlworld.com> writes
>
>From: Raj Jammalamadaka <cppuser2002 at yahoo.com>
>
>> Except for friendship, inheritance is the strongest
>> relationship that can be expressed in C++ and should
>> be used only when it’s necessary.
>
>Here's a slightly interesting one - is friendship stronger than inheritance?

No. Hasn't been in the past and isn't now.

>In one way, yes: a friend has full access to a class, whereas a derived 
>class can't see the base's private members.

Intimate, but specific and local. Friendship is constrained, derived 
classes are not.

>In another way, no: to the client, the friend is just another 
>class/method, whereas the derived class IsA base class, with all the 
>implicit conversions implied.

Inheritance is a significantly stronger coupling relationship than 
friendship. At least Herb is consistent in getting the ranking slightly 
wrong, as it this ranking is mentioned in other books. Just examine the 
consequence of the two relationships on a real (or indeed, imagined) 
source base and see what happens. The effect of ill-considered 
inheritance is far more pronounced than ill-considered friendship, and 
likewise the effect of any changes.

Kevlin
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