purity and memory allocations/pointers

[John Colvin]

On Saturday, 3 August 2013 at 21:19:35 UTC, monarch_dodra wrote:
> On Saturday, 3 August 2013 at 19:07:49 UTC, Meta wrote:
>> On Saturday, 3 August 2013 at 16:47:52 UTC, Timon Gehr wrote:
>>> On 08/03/2013 05:59 PM, monarch_dodra wrote:
>>>> One last question: Pointers.
>>>>
>>>> int get(int* p) pure
>>>> {
>>>>   return *p;
>>>> }
>>>>
>>>> void main()
>>>> {
>>>>   int i = 0;
>>>>   auto p = &i;
>>>>   get(p);
>>>> }
>>>>
>>>> Here, get, to me, is obviously not pure, since it depends on 
>>>> the state
>>>> of the global "i". *Where* did "get" go wrong? Did I simply 
>>>> "abusively"
>>>> mark get as pure? Is the "pure" keyword's guarantee simply 
>>>> "weak"?
>>>> ...
>>>
>>> Yes, it's weak.
>>
>> It depends on whether you think a pointer dereference is pure 
>> or not (I don't know the answer). That aside, as long as get 
>> doesn't modify the value at *p or change what p points to, 
>> this is strongly pure (i.e., the academic definition of 
>> purity).
>
> Thank the 3 of you for your answers. I think I had a wrong 
> preconception of what pure is. I think this cleared most of it 
> up.

Is there anywhere formal defining D's pure (weak vs strong etc.)? 
A page in the wiki perhaps?

Imagine someone new coming to D and being confused by what our 
purity system is. It would suck to only be able to give an ad-hoc 
answer or link them to a previous discussion.

I would offer but I don't really understand it myself.