defining "in" What is the proper way in D2?

[Timon Gehr]

On 09/12/2011 04:17 PM, Steven Schveighoffer wrote:
> On Mon, 12 Sep 2011 10:10:35 -0400, Simen Kjaeraas
> <simen.kjaras at gmail.com> wrote:
>
>> On Mon, 12 Sep 2011 00:11:11 +0200, Timon Gehr <timon.gehr at gmx.ch> wrote:
>>
>>> I think the fact that "in" for AAs returns a pointer is a mistake and
>>> ugly in the first place and any generic code that relies on any
>>> container to return a raw internal pointer is flawed by itself imho.
>>
>> If D had a Nullable struct, that would likely be a much better return
>> type for 'in'. The thing is, we do have a nullable!T type: T*.
>>
>> This is simply a case of having a wrench and needing a hammer.
>
> No, the advantage of using a pointer is, you can change the value
> without incurring another lookup. A nullable struct does not have that
> advantage.

A decent compiler has that advantage without requiring programmers to 
abuse the 'in' operator.

>
> I think the correct return type for that should be a cursor (i.e. a
> single-element range which can be used to refer to that element at a
> later time). This allows even more functionality, such as removing the
> element, or referring to both the key and value.
>

The correct return type for 'in' is bool. But the functionality you 
propose could be quite useful indeed.