DIP6: Attributes

[Ary Borenszweig]

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]