Is This a Bug

[Timon Gehr]

On 10/26/2011 07:01 PM, Jonathan M Davis wrote:
> On Wednesday, October 26, 2011 03:04 bearophile wrote:
>> Jonathan M Davis:
>>> On Wednesday, October 26, 2011 11:15:20 Gor Gyolchanyan wrote:
>>>> I see. But is there any practical advantage of a function being pure?
>>>> I mean, besides an optimization hint for the compiler, of course.
>>>
>>> 1. You know that it doesn't access global variables, which is at minimum
>>> an advantage as far as understanding the code goes.
>>
>> The lack of side effects makes it (maybe) less hard to understand code,
>> makes testing and unit testing simpler, and allows some optimizations,
>> like replacing filter(map()) with a map(filter())...
>>
>> In DMD 2.056 several functions and higher order functions like array(),
>> map(), filter(), etc, aren't (always) pure, so I think D/Phobos purity
>> needs a bit of improvement. This compiles:
>>
>> import std.algorithm;
>> void main() pure {
>> int[] a;
>> map!((int x){ return x; })(a);
>> map!((x){ return x; })(a);
>> }
>>
>>
>> This doesn't:
>>
>> import std.algorithm, std.array;
>> void main() pure {
>> int[] a;
>> map!q{ a }(a);
>> filter!q{ a }(a);
>> array(a);
>> int[int] aa;
>> aa.byKey();
>> aa.byValue();
>> aa.keys;
>> aa.values;
>> aa.get(0, 0);
>> aa.rehash;
>> }
>
> That's because the functions for associative arrays haven't been fixed up for
> purity yet. It'll happen. The situation with pure has already improved
> drastically over the last few releases.
>
> - Jonathan M Davis

map!q{ a }(a); fails purity validation too.
That is possibly a compiler bug.