Erlang/OTP R10B-10 has been released

Bengt Kleberg <>
Tue Mar 21 14:24:16 CET 2006


On 2006-03-21 08:54, Matthias Lang wrote:
...deleted
> 
> Another thing. A major use of the preprocessor is conditional
> compilation, e.g. 
> 
>   -ifdef(POLITICALLY_CORRECT)
>   pi() -> 3.0.
>   -else.
>   pi() -> 3.14159.
>   -endif.
> 
> That can cause confusion along the lines of "am I debugging the code
> I'm looking at", but how else do you solve that problem? 

since this (conditional compilation) is very difficult to manage i will 
try to come up with something that is atleast different.

how about:
pi(politically_correct) -> 3.0;
pi(_) -> 3.14159.

you will need an extra variable for all functions call chains that are 
''different'' somewhere.


> The standard advice is to put the variant code in seperate
> modules. Doing that has quite a disruptive effect on a program's
> organisation---the classic example is that you have a working system
> on hardware X and now you want to extend it to work on hardware
> Y. Your choices are now
> 
>   a) Use conditional compilation and sprinkle changes throughout
>      the code. Ugly because it uses the preprocessor and because
>      code gets twice as long in many seperate places. Nice because
>      it's fairly easy to convince yourself that you haven't broken
>      the system for X.

in the past ('85-'90) i tried this when programming in c. unfortunatly 
it was only myself i convinced about not breaking X. the software i 
wrote was often broken for X.


>   b) Re-structure the system so that there's a layer of redirection
>      ("abstraction") which takes care of the differences between X and
>      Y. Nice because it avoids the preprocessor. Ugly because it's
>      harder to avoid creating double-maintenance problems and ugly
>      because its more likely, in my experience, to introduce bugs
>      to the otherwise 'stable' X target.

after '93 i tried to put the c code for X and the c code for Y into 
different source files, and link with the right verison. it worked 
better for me. ie, i had less maintenance problems and less bugs in the 
'stable' X target.

ymmv.


bengt



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