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

[Steven Schveighoffer]

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.

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.

-Steve