Null references redux

[Denis Koroskin]

On Sun, 27 Sep 2009 02:03:40 +0400, Walter Bright
<newshound1 at digitalmars.com> wrote:

> Denis Koroskin wrote:
>> 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
>
> d is initialized to the "invalid" unicode bit pattern of 0xFFFF. You'll  
> see this if you put a printf in. The bug here is in writeln failing to  
> recognize the invalid value.
>
> http://d.puremagic.com/issues/show_bug.cgi?id=3347
>

Change dchar to float or an int. It's still not initialized (well,
default-initialized to some garbage, which may or may not be okay for a
programmer).

>> I don't see at all how is it related to a non-null default.
>
> Both are attempts to use invalid values.
>

No.

>> Non-null default is all about avoiding erroneous situations, enforcing  
>> program correctness and stability. You solve an entire class of  
>> problem: NullPointerException.
>
> No, it just papers over the problem. The actual problem is the user  
> failed to initialize it to a value that makes sense for his program.  
> Setting it to a default value does not solve the problem.
>
> Let's say the language is changed so that:
>
>     int i;
>
> is now illegal, and generates a compile time error message. What do you  
> suggest the user do?
>
>     int i = 0;
>

1) We are talking about non-null *references* here.
2) I'd suggest user to initialize it to a proper value.

"int i;" is not the whole function, is it? All I say is "i" should be
initialized before accessed, and that fact should be statically enforced
by a compiler.

> The compiler now accepts the code. But is 0 the correct value for the  
> program? I guarantee you that programmers will simply insert "= 0" to  
> get it to pass compilation, even if 0 is an invalid value for i for the  
> logic of the program. (I guarantee it because I've seen it over and  
> over, and the bugs that result.)
>

This is absolutely irrelevant to non-null reference types. Programmer  
can't write
"Object o = null;" to cheat on the type system.