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

[Charles Hixson]

On 09/11/2011 02:12 PM, Jonathan M Davis wrote:
> On Sunday, September 11, 2011 14:00:55 Charles Hixson wrote:
>> On 09/11/2011 01:25 PM, Vladimir Panteleev wrote:
>>> On Sun, 11 Sep 2011 23:02:37 +0300, Charles Hixson
>>>
>>> <charleshixsn at earthlink.net>  wrote:
>>>> I can't figure it out from
>>>> http://www.digitalmars.com/d/2.0/operatoroverloading.html#Binary
>>>
>>> // I assume your data structure looks like this
>>> class Node(Key, Data)
>>> {
>>> Key k;
>>> Node!(Key, Data) left, right;
>>> int level;
>>> // ...
>>>
>>> void opBinary!("in")(Key k)
>>> {
>>> if (level == 0) return false;
> Path: digitalmars.com!not-for-mail
> From: Charles Hixson<charleshixsn at earthlink.net>
> Newsgroups: digitalmars.D.learn
> Subject: Re: defining "in"  What is the proper way in D2?
> Date: Sun, 11 Sep 2011 14:09:57 -0700
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>
> On 09/11/2011 01:33 PM, David Nadlinger wrote:
>> On 9/11/11 10:25 PM, Vladimir Panteleev wrote:
>>> void opBinary!("in")(Key k)
>>
>> Shouldn't that be »void opBinary(string op : "in")(Key k)«? Also, you
>> probably want to use opBinaryRight, because opBinary hooks »if
>> (container in key)«.
>>
>> David
>
> And thanks for THIS, too.  I'd just started to wonder about the order of
> the syntax.  After all, the key is in the container, but not conversely.
>
>>> if (k<  key) return k in left;
>>> if (key<  k) return k in right;
>>> return true;
>>> }
>>> }
>>
>> VOID??  I'm going to presume that this should have been bool.
>> Otherwise, thanks.  That was they syntax I couldn't figure out from the
>> docs.
>>
>> And, yeah.  That's what it looks like.  My find code was wrong, because
>> it should have referenced the node, so what I need to do is move the cod
>> into the node class.  But it was the syntax of defining the opBinary
>> specialization that was hanging me up.  (For some reason I have a hard
>> time wrapping my mind around template code.)
>
> The "in" operator normally returns a pointer to the value that you're trying
> to find (and returns null if it's not there). Making it return bool may work,
> but it's going to be a problem for generic code. That's like making
> opBinary!"*" return a type different than the types being multiplied. It's just
> not how the operator is supposed to be used and could cause problems.
>
> - Jonathan M Davis

OK, but what if the container is supposed to be opaque to external 
observers, but you still want to be able to tell whether it contains a 
particular item?  Doesn't returning a pointer violate encapsulation?

Also, the compiler complained about the declaration, causing me to 
currently substitute, thus:

// bool opBinaryRight!("in")(Key k)
    bool opBinaryRight(string op)(Key k) if (op == "in")

I swiped that code from std.container.d  (which also returns a bool). 
As what I'm doing is pretty much like a standard container, this seemed 
like a reasonable place to look.  I sure hope that this doesn't mean I 
need to instantiate every use of in.  If that's the case I might be 
better off just staying with find.