Null references redux

[Denis Koroskin]

On Sun, 27 Sep 2009 01:08:32 +0400, Walter Bright  
<newshound1 at digitalmars.com> wrote:

> Denis Koroskin wrote:
>  > On Sat, 26 Sep 2009 22:30:58 +0400, Walter Bright
>  > <newshound1 at digitalmars.com> wrote:
>  >> D has borrowed ideas from many different languages. The trick is to
>  >> take the good stuff and avoid their mistakes <g>.
>  >
>  > How about this one:
>  >  
> http://sadekdrobi.com/2008/12/22/null-references-the-billion-dollar-mistake/  
>  >
>  >
>  > :)
>
> I think he's wrong.
>
> Getting rid of null references is like solving the problem of dead  
> canaries in the coal mines by replacing them with stuffed toys.
>
> It all depends on what you prefer a program to do when it encounters a  
> program bug:
>
> 1. Immediately stop and produce an indication that the program failed
>
> 2. Soldier on and silently produce garbage output
>
> I prefer (1).
>
> Consider the humble int. There is no invalid value such that referencing  
> the invalid value will cause a seg fault. One case is an uninitialized  
> int is set to garbage, and erratic results follow. Another is that (in  
> D) ints are default initialized to 0. 0 may or may not be what the logic  
> of the program requires, and if it isn't, again, silently bad results  
> follow.
>
> Consider also the NaN value that floats are default initialized to. This  
> has the nice characteristic of you know your results are bad if they are  
> NaN. But it has the bad characteristic that you don't know where the NaN  
> came from. Don corrected this by submitting a patch that enables the  
> program to throw an exception upon trying to use a NaN. Then, you know  
> exactly where your program went wrong.
>
> It is exactly analogous to a null pointer exception. And it's darned  
> useful.

I don't understand you. You say you prefer 1, but describe the path D  
currently takes, which is 2!

dchar d; // not initialized
writeln(d); // Soldier on and silently produce garbage output

I don't see at all how is it related to a non-null default.

Non-null default is all about avoiding erroneous situations, enforcing  
program correctness and stability. You solve an entire class of problem:  
NullPointerException.