Short list with things to finish for D2

[Justin Johansson]

Andrei Alexandrescu wrote:
> Justin Johansson wrote:
>> 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.
> 
> I disagree with this false choice.
> 
> http://en.wikipedia.org/wiki/False_dilemma#False_choice
> 
> 
> Andrei

You are very well read :-)