Re: Building blocks (Was: Design By Contract)

[Stephen Leake <Stephen.Leake@gsfc.nasa.gov>]

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