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

[Charles Hixson]

On 09/11/2011 04:07 PM, Timon Gehr wrote:
> 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
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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)
>
> 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?
>
>
>
>
>
container.binaryOp("in")!(something I haven't figured out yet.

Template syntax doesn't make any sense to me yet.  I'm just copying 
examples and adapting them with a cut and try and see what works and 
what doesn't.  More failures than successes.

OTOH, it does seem better than C++ template syntax, but that's VERY 
faint praise indeed.