Writing Bug-Free C/D Code

[Knud Soerensen]

On Mon, 19 Mar 2007 11:44:54 +0100, Henning Hasemann wrote:

> 
> I sometimes have some problems with this, as said before: Let SDL return
> a width as uint and have your positions int (because they also can be negative).
> 
> I had this problems with C already. Examples of questions I have often when coding:
> - "Hmm okay. You're a on-screen coordinate. You will be positive.
>   But I might to want to mix you with virtual and potetially negative
>   Coordinates. Also you wont be larger than 32000, as long as screens
>   wont get really big. But I somehow feel I should make you an int..."
> - Hm okay so I have these few things I know of they wont be negative.
>   Should I make them int nevertheless? Would avoid complications and warinings,
>   and the value range wouldnt be a problem.

Well, I think your problems is due to fundamental errors in your
programming method. :-)

We all know the ordinary form of Hungarian notation as described in
http://www.duckware.com/bugfreec/chapter3.html#naming
but there is also a stronger form called app-Hungarian notation
where the prefix gives a hint of the purpose for the variable.
Like rowPos for a row position and colPos for a column position.
Now it is easy to spot buggy code like rowPos=colPos etc.

Using a type system we can take the idea a step further.

typedef int ROWPOS;
typedef int COLPOS;

foo 
{
  ROWPOS rowPos;
  COLPOS colPos;
 
  rowPos = colPos; // error at compiler time.
}

So, the fundamental flaw is that you use raw types instead
of making a type for each purpose in your code.

Could the compiler do something about it ?
Yes, it could provide a switch called -bugfree 
which trows a error every time a non user defined type is
used in the code.

It would also be useful if we could add an invariance to the type
instead of have to change it into a class or structure.