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From: Stephen Leake <Stephen.Leake@gsfc.nasa.gov>
Subject: Re: Building blocks (Was: Design By Contract)
Date: 1997/10/03
Message-ID: <3434F608.3E02@gsfc.nasa.gov>#1/1
X-Deja-AN: 277603511
References: <34316EC3.5B62@dynamite.com.au>
 <199710011402.QAA02444@basement.replay.com> <EHFvt5.D1G@world.std.com>
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Reply-To: Stephen.Leake@gsfc.nasa.gov
Newsgroups: comp.lang.ada
Date: 1997-10-03T00:00:00+00:00
List-Id: <comp.lang.ada>


Robert A Duff wrote:

> By the way, speaking of negative logic, what do people think about
> negative logic in "if" statements?  I tend to try to reduce the number
> of "not"s in the code.  But other people tend to use some other
> heuristic, such as "do the normal case first" or "do unusual case
> first".  For example:
> 
>     if Is_Evil(X) then
>         print error message;
>     else
>         ... -- 37 lines of code doing the normal thing
>     end if;

I prefer this style; put the easily handled case first.

> 
> vs
> 
>     if not Is_Evil(X) then
>         ... -- 37 lines of code doing the normal thing
>     else
>         print error message;
>     end if;
> 
> vs
> 
>     if Is_Good(X) then
>         ... -- 37 lines of code doing the normal thing
>     else
>         print error message;
>     end if;
> 
> vs
> 
>     if not Is_Good(X) then
>         print error message;
>     else
>         ... -- 37 lines of code doing the normal thing
>     end if;
> 
> Or perhaps even:
> 
>     if Is_Evil(X) then
>         print error message;
>         return;
>     end if;
>     ... -- 37 lines of code doing the normal thing

I also do this, especially when the 'return' gets me out of more than
one layer of 'if'

> 
> - Bob

-- 
- Stephe