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

[Timon Gehr]

On 09/12/2011 12:28 AM, Charles Hixson wrote:
> 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
>> Organization: Digital Mars
>> Lines: 15
>> Message-ID:<j4j83k$ree$1 at digitalmars.com>
>> References:<j4j45h$iti$1 at digitalmars.com>
>> <op.v1nu0fdrtuzx1w at cybershadow.mshome.net> <j4j5uq$m8n$1 at digitalmars.com>
>> Mime-Version: 1.0
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>> Content-Transfer-Encoding: 8bit
>> X-Trace: digitalmars.com 1315775412 28110 66.245.57.66 (11 Sep 2011
>> 21:10:12 GMT)
>> X-Complaints-To: usenet at digitalmars.com
>> NNTP-Posting-Date: Sun, 11 Sep 2011 21:10:12 +0000 (UTC)
>> User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US;
>> rv:1.9.2.21) Gecko/20110831 Iceowl/1.0b2 Icedove/3.1.13
>> In-Reply-To:<j4j5uq$m8n$1 at digitalmars.com>
>> Xref: digitalmars.com digitalmars.D.learn:29434
>>
>> 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)

That is not valid syntax and probably will never be.

> 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 agree.


> 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.

How do you mean, instantiate it?