thoughts on immutability in D

[Steven Schveighoffer]

On Fri, 23 Sep 2011 20:13:39 -0400, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 9/23/2011 4:13 PM, Jonathan M Davis wrote:
>> But while C++'s const is not as good as D's const, it's still very  
>> worthwhile
>> IMHO.
>
> To me it's like buffer overflows. 99% of C/C++ code doesn't have buffer  
> overflows, and is perfectly reliable. But if someone hands you a  
> 1,000,000 line program and asks "ensure there are no buffer overflows"  
> what are you going to do? What are you going to do when Junior  
> Programmer makes a patch to your perfectly correct C/C++ code base, and  
> now it has a subtle overflow bug? Start all over with the review process?
>
> This is not an idle question, as a major focus of C static analysis  
> tools is to detect buffer overflows, and people spend a lot of effort &  
> money on them.
>
> Faith based programming works in the small, but programs grow ever  
> larger in size and complexity. Switching from faith to static guarantees  
> is a much more scalable technique.
>
> And where C++ const is really, really useless is when it comes to  
> multithreaded programming.

D's const system is also not impervious to Junior mistakes (even without  
casts!), but it's certainly better than C++.

The truth is, the only time you get guarantees with D is when you have  
pure functions and immutable data.  Const doesn't guarantee anything.   
Even immutable functions still can access global state.

-Steve