alias this + std.array.popFront

[Tobias Pankrath]

On Saturday, 30 March 2013 at 00:23:17 UTC, Jonathan M Davis 
wrote:
> On Friday, March 29, 2013 23:22:36 Tobias Pankrath wrote:
>> On Friday, 29 March 2013 at 22:13:31 UTC, Tobias Pankrath 
>> wrote:
>> > Hello,
>> > 
>> > the following struct is not an input range because you can't
>> > call popFront on it, however I'd say you should be able to.
>> > 
>> > struct Wrapper {
>> > 
>> > int[] _data;
>> > alias _data this;
>> > 
>> > }
>> > 
>> > Bug or intended behaviour?
>> > 
>> > Thank you!
>> 
>> The reason seems to be that, while 
>> is(DynamicArrayTypeOf!Wrapper
>> == int[]) holds, isDynamicArray!Wrapper equals false, because
>> isDynamicArray checks for !isAggregateType!Wrapper. Looks like 
>> a
>> bug isDynamicArray to me.
>
> No, it is most definitely _not_ a bug in isDynamicArray. The 
> isX traits in
> std.traits specifically check for exact tyes and _not_ implicit 
> conversions. If
> it's a bug, it's in the fact that isDynamicArray is used in 
> popFront's
> template constraint. Whether or not Wrapper should be treated 
> as a range is up
> for some debate (implicit conversion tends to cause big 
> problems with template
> constraints, as it becomes far too easy to have constraints 
> which pass and yet
> the function doesn't actually work with the type), but the main 
> problem is
> that front and popFront for arrays don't agree on what they 
> should work with -
> front takes T[] and popFront checks isDynamicArray. So, front 
> works with
> implicit conversion, and popFront doesn't, and that needs to be 
> fixed. But the
> bug is in front/popFront, not isDynamicArray.
>
> I believe that there was a thread on this recently (started by 
> monarch_dodra
> IIRC), so you can look for that discussion for more information 
> if you'd like.
>
> - Jonathan M Davis

Yes, you are most probably right that the bug is not in 
isDynamicArray. However DynamicArrayTypeOf and isDynamicArray are 
rather inconsistent since DynamicArrayTypeOf does not check exact 
types.