Short list with things to finish for D2

[Justin Johansson]

Justin Johansson wrote:
> aarti_pl wrote:
>> Andrei Alexandrescu pisze:
>>> aarti_pl wrote:
>>>> aarti_pl pisze:
>>>>> Andrei Alexandrescu pisze:
>>>>>> 2. User-defined operators must be revamped. Fortunately Don 
>>>>>> already put in an important piece of functionality (opDollar). 
>>>>>> What we're looking at is a two-pronged attack motivated by Don's 
>>>>>> proposal:
>>>>>>
>>>>>> http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP7
>>>>>>
>>>>>> The two prongs are:
>>>>>>
>>>>>> * Encode operators by compile-time strings. For example, instead 
>>>>>> of the plethora of opAdd, opMul, ..., we'd have this:
>>>>>>
>>>>>> T opBinary(string op)(T rhs) { ... }
>>>>>>
>>>>>> The string is "+", "*", etc. We need to design what happens with 
>>>>>> read-modify-write operators like "+=" (should they be dispatch to 
>>>>>> a different function? etc.) and also what happens with 
>>>>>> index-and-modify operators like "[]=", "[]+=" etc. Should we go 
>>>>>> with proxies? Absorb them in opBinary? Define another dedicated 
>>>>>> method? etc.
>>>>>>
>>>>>> * Loop fusion that generalizes array-wise operations. This idea of 
>>>>>> Walter is, I think, very good because it generalizes and 
>>>>>> democratizes "magic". The idea is that, if you do
>>>>>>
>>>>>> a = b + c;
>>>>>>
>>>>>> and b + c does not make sense but b and c are ranges for which 
>>>>>> a.front = b.front + c.front does make sense, to automatically add 
>>>>>> the iteration paraphernalia.
>>>>>>
>>>> (..)
>>>>>> Andrei
>>>>>
>>>>> I kinda like this proposal. But I would rather call template like 
>>>>> below:
>>>>>
>>>>> T opInfix(string op)(T rhs) { ... }
>>>>> T opPrefix(string op)(T rhs) { ... }
>>>>> T opPostfix(string op)(T rhs) { ... }
>>>>>
>>>>> and allow user to define her own operators (though it doesn't have 
>>>>> to be done now).
>>>>>
>>>>> I know that quite a few people here doesn't like to allow users to 
>>>>> define their own operators, because it might obfuscate code. But it 
>>>>> doesn't have to be like this. Someone here already mentioned here 
>>>>> that it is not real problem for programs in C++. Good libraries 
>>>>> don't abuse this functionality.
>>>>>
>>>>> User defined operators would allow easy definition of Domain 
>>>>> Specific Languages in D. I was already writing about it some time ago:
>>>>>
>>>>> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81026 
>>>>>
>>>>> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81352 
>>>>>
>>>>>
>>>>> BR
>>>>> Marcin Kuszczak
>>>>> (aarti_pl)
>>>>
>>>> Of course for opPrefix/opPostfix signatures will be different:
>>>> T opPrefix(string op)() { ... }
>>>> T opPostfix(string op)() { ... }
>>>>
>>>> Sorry for mistake.
>>>>
>>>> BR
>>>> Marcin Kuszczak
>>>> (aarti_pl)
>>>
>>> I think we'll solve postfix "++" without requiring the user to define 
>>> it. Do you envision user-defined postfix operators?
>>>
>>> Andrei
>>
>> Well, maybe something like below:
>>
>> auto a = 2²;  //(quadratic power of 2)
>> auto a = 5!;  //factorial of 5
>> auto a = 2Ƴ + 3ɛ; //solving equations
>> auto weight = 5kg; //units of measurement
>>
>> The point is that this covers whole scope of operators. In fact even 
>> built-in operators could be defined using it.
>>
>> Postfix operator ++ can be defined using prefix operator++ just by 
>> delegation and this can be default.
>>
>> Best Regards
>> Marcin Kuszczak
>> (aarti_pl)
> 
> Marcin demonstrates a valid point.
> 
> If there is going to be this feature creep, the feature should be 
> complete with all the usual variants of operator arity and notation 
> (i.e. prefix/postfix/infix).  Otherwise it really it's only two-thirds 
> baked.
> 
> -- Justin Johansson

I meant to say "Iff there is ..." as in "if and only if".

Like others, I'm not completely sold on the idea at all.  Also it's 
probably not possible to squeeze something as long as this on to a short 
list.

All or nothing please.