From: Mark Wooding <mdw@distorted.org.uk>
Date: Sat, 9 Jun 2018 02:49:35 +0000 (+0100)
Subject: doc/intro.tex: Strengthen the argument about C++ a bit.
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/sod/commitdiff_plain/4f94eb86e2a250e79f73c16da772c91bf0795708

doc/intro.tex: Strengthen the argument about C++ a bit.
---

diff --git a/doc/intro.tex b/doc/intro.tex
index f77eed0..3e5e8f7 100644
--- a/doc/intro.tex
+++ b/doc/intro.tex
@@ -143,10 +143,13 @@ which is unlikely to be what was wanted: `B' prints twice, and the `before'
 and `after' actions are both in the middle.\footnote{%
   Of course, one could have arranged to call @|Y::f| before @|X::f| -- but
   the important point is that one would have needed to \emph{know} that this
-  was necessary.} %
+  was necessary.  And you still end up with two copies of `B'.} %
 The problem is that correctly composing behaviour from a collection of
 superclasses requires knowledge of all of the superclasses involved and how
-they're supposed to work together.
+they're supposed to work together.  Messing with virtual base classes has
+eliminated the problem of duplicating @|B|'s state, but has done nothing to
+help avoid duplicating @|B|'s \emph{behaviour} -- which is a shame, because
+duplicating one without the other is going to end badly.
 
 The obvious workaround is to separate the functionality -- here, printing the
 messages -- from the plumbing, which arranges to do everything in the right