DIP6: Attributes

[Ary Borenszweig]

Don wrote:
> Ary Borenszweig wrote:
>> Don escribió:
>>> grauzone wrote:
>>>> Don wrote:
>>>>> Ary Borenszweig wrote:
>>>>>> http://www.prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP6
>>>>>
>>>>> This looks like a solution in search of a problem. What's the 
>>>>> problem being solved?
>>>>
>>>> Attaching additional data to types, that can't be specified 
>>>> otherwhere. This should help with metaprogramming-like stuff.
>>>>
>>>> For example serialization. How do you specify that a field shouldn't 
>>>> be part of the serialized data? Java has an extra keyword attribute 
>>>> like
>>>> "transient" (comes from before attributes were introduced). C# uses 
>>>> what we call annotation in this thread. How would you do this in D?
>>>
>>> I agree that there doesn't seem to be a nice way at present. One 
>>> possibility would be to establish a naming convention for transient 
>>> fields -- a Ruby-style solution, I guess.
>>>
>>> But are annotations actually an ideal solution for this problem?
>>> Presumably, you'll have to specify that somewhere else anyway. I 
>>> mean, during reading it will need to either be initialized separately 
>>> after serialisation (like opPostBlit, perhaps?), or else remain 
>>> uninitialized. Serialisation seems to be _extremely_ similar to 
>>> construction. I'm not sure that annotations capture that.
>>>
>>> D has much more powerful metaprogramming than C# or Java, so my 
>>> intuition and hope is that we shouldn't need to adopt hacks from 
>>> those weaker languages. The annotation syntax in C# and Java looks 
>>> like an ugly hack to me. Purely a subjective opinion, of course, but 
>>> it seems really out of place in a C-family language.
>>
>> Attributes has many, many other uses. Appart from serialization, you 
>> could specify how a field is stored in a database. How a method maps 
>> to an http request (post, get, which parameters to bind to the 
>> request, etc.). Whether a method should do security checks before 
>> executing. Whether a method should be run as a test, and what's the 
>> expected exception to be thrown. [insert your usage here]
> 
> Great, you've answered my question. That should be in the DIP, instead 
> of the vague stuff that's in there now -- the existing DIP is about 
> replacing keywords, which is very unconvincing. (It doesn't work, 
> actually -- the name mangling is important for most of the keywords 
> mentioned).

But the DIP I wrote isn't about general-purpose annotations. It's just 
the first step. Are "pure" and "nothrow" part of the mangling? Or which 
are? I thought not. Can you overload a pure and a not-pure function with 
the same parameter count and types?

Anyway, I'll write some more about attributes in the abstract or rationale.