thoughts on immutability in D

[Mehrdad]

On 9/23/2011 8:11 PM, Jonathan M Davis wrote:
> On Friday, September 23, 2011 19:42:24 Walter Bright wrote:
>> On 9/23/2011 6:55 PM, Jonathan M Davis wrote:
>>> True, but it doesn't just happen. You have to choose to make a variable
>>> mutable.
>> Which you *must* do for logical const. And, of course, anything beyond the
>> first level is not const at all, and there's NO WAY to say it is const.
>>
>>> _Some_ effort must be put in to circumvent const. Until you do that,
>>> const protects it from be changed.
>> There's no way to detect who or what is changing it.
>>
>>> By no means am I claiming that C++'s const is without flaws. I'm just
>>> claiming that it's not worthless, and you seem to be claiming that it's
>>> worthless.
>> I think it is worthless because:
>>
>> 1. a number of C++ programmers I've talked to who relied on being able to
>> change const objects and insisted that was a feature.
>>
>> 2. the pervasive misconceptions about what C++ const guarantees and what it
>> doesn't, even among C++ committee members.
>>
>> 3. the complete uselessness C++ const has for multithreaded programming.
>>
>> 4. the pervasiveness of the Double Checked Locking Bug, which is one of the
>> consequences of (3).
>>
>> 5. it's head-const only. Anything beyond one level of indirection is
>> completely const-free. Only trivial data structures are one level.
> Well, I grant you that all of those are issues, but I don't think that they
> makes C++'s const worthless. Const has caught bugs in my code for me. I have
> found it to be useful in the projects that I've worked on. So, we're obviously
> just going to have to agree to disagree on this, and I think that a lot of C++
> programmers are going to disagree with you (including many who understand
> exactly what const does and doesn't guarantee).
>
> - Jonathan M Davis
+1 gotta agree 100% with Jon here. (Hey, is that the first time?! :P) I 
wouldn't believe anyone for 1 second if he said he's used const in his 
code and it never caught an error for him (or if it introduced more than 
it caught).