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

[Steven Schveighoffer]

On Mon, 12 Sep 2011 10:24:52 -0400, Timon Gehr <timon.gehr at gmx.ch> wrote:

> 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.

I agree the term 'in' doesn't accurately describe the function I propose.   
But then again, AA doesn't provide any other means to avoid  
double-lookup.  I think having a different member function to do the same  
thing, and re-purposing 'in' to just return bool would be fine.  This  
should be entirely possible, since AA's are now at least extendable by the  
library.

-Steve