On 06/03/10 14:39, Steinar Bang wrote:
Larry Evans <cppljev...@suddenlink.net>:
claims that switch statements are faster than virtual function calls.
That's not really interesting, is it? The overhead and downsides of
virtual functions are well known.
The upside is the possibility to use polymorphism to make frameworks.
All kinds of pluggable frameworks.
And as polymorphism goes, virtual functions are pretty cheap.
Agreed; however, according the the 2nd link I provided:
http://lists.boost.org/Archives/boost/2008/01/132074.php
apparently speed is more important, and the 1st link:
http://sourceforge.net/mailarchive/message.php?msg_name=3f49a9f41003031715g19a23b94p47ccec2251acd55%40mail.gmail.com
suggested that the author had experienced problems with
using switch vs virtual functions:
P.P.S. Yes, the design you are using is a sore spot for me, I was bit
with such things many years ago, it is one of my quests to educate
people about the better ways now.
I'd had some experience with compilers written in c++ that had large
switch statements and wondered why the authors hadn't used virtual
functions. IOW, I believed as you do; however, OvermindDl1's post
caused me some doubt. I even checked clang's code to see if they used
switch's or virtual functions and was surprised to learn they used
switch's:
http://llvm.org/svn/llvm-project/cfe/trunk/lib/Analysis/CFG.cpp
(in particular, the CFGBuilder::Visit function).
Hence, I figured there must be something I'm missing
about the pros and cons of switch's vs virtual functions.
-regards,
Larry
