On Friday, January 21, 2011 12:36:23 Ary Manzana wrote: > On 1/20/11 5:48 PM, Jacob Carlborg wrote: > > On 2011-01-20 21:34, Steven Schveighoffer wrote: > >> On Thu, 20 Jan 2011 15:03:55 -0500, Jacob Carlborg <d...@me.com> wrote: > >>> On 2011-01-20 19:18, Steven Schveighoffer wrote: > >>>> On Thu, 20 Jan 2011 13:07:58 -0500, Jacob Carlborg <d...@me.com> wrote: > >>>>> On 2011-01-20 15:02, Steven Schveighoffer wrote: > >>>>>> On Thu, 20 Jan 2011 08:47:28 -0500, Justin Johansson <j...@nospam.com> > >>>>>> > >>>>>> wrote: > >>>>>>> Not long ago the Java Language people introduced the idea of > >>>>>>> annotations together with an annotation processing tool (apt). > >>>>>>> > >>>>>>> Now perhaps the idea of source code annotations is not actually a > >>>>>>> Java > >>>>>>> invention per se, however for someone learning D is there any > >>>>>>> equivalent idiom [of Java annotations] in the D language? > >>>>>> > >>>>>> Haven't used Java since they added annotations, but I think they are > >>>>>> like C# attributes? > >>>>>> > >>>>>> In any case, D has an annotation syntax like: > >>>>>> > >>>>>> @property > >>>>>> > >>>>>> But I think at the moment, annotations have no custom ability. Only > >>>>>> compiler-defined annotations are allowed. This may change in the > >>>>>> future, > >>>>>> but probably not short-term. FWIW, I think we need a much richer > >>>>>> runtime-reflection capability before we can use custom annotations > >>>>>> to any great effect. > >>>>>> > >>>>>> -Steve > >>>>> > >>>>> I would rather formulate it like: currently D has a syntax for > >>>>> keywords that are similar to Java annotations. > >>>> > >>>> I don't think it's the same thing. Keywords are not allowed to be used > >>>> anywhere else, even for things that would parse properly were they not > >>>> keywords. They are anchors for the parser to determine where it is. In > >>>> contrast, a compiler-defined annotation is parsed just the same as a > >>>> custom one, it's just that the meaning is predefined. > >>>> > >>>> For example, you can legally do: > >>>> > >>>> int property; > >>>> > >>>> without error, but this won't even get past the parsing stage: > >>>> > >>>> int struct; > >>>> > >>>> -Steve > >>> > >>> I assume you meant "int @property;"? > >> > >> No. I meant int property; > > > > Of course that would work, isn't that like saying this won't work: > > > > int struct_; // ? > > > >> A keyword is specifically not allowed where the grammar would otherwise > >> allow it. A symbol isn't allowed to have @ in it, so this naturally > >> prevents a conflict. I realize the poor example, but it's definitely not > >> a keyword. Otherwise, it would be listed here: > >> http://www.digitalmars.com/d/2.0/lex.html#keyword (actually, are > >> annotations part of the lexical grammar there?). > >> > >> It's more like Object, which is not a keyword, but you aren't allowed to > >> use it to mean anything besides what it means. > >> > >> The end result is, it fails if you use it in the wrong place, but the > >> keyword status makes it fail at the parsing stage. I am not a compiler > >> writer, so I'm talking a bit from my ass here. > >> > >> -Steve > > > > Ok, maybe you're right. I'm pretty sure, as you say, that a keyword in > > the wrong place would fail during parsing. But I don't know where a > > misplaced annotation/attribute would fail. > > Jacob is right here. > > This, as you say, fails: > > int struct; > > And also this fails: > > int @property; > > So yes, currently @property is just a keyword with a prepended @. > > Annotations in Java anc C# can have arguments. That is not the case in > D. For example, as it is said in DIP6, you could have: > > @extern('C') > void someFunc(); > > instead of having extern a keyword and thus being unable to use it for > identifiers.
No. No attributes are keywords. The reasoning is simple. A keyword is a word that would be a valid identifier but isn't, because the language treats it as special. @ is not a valid part of an identifier. So, @property can't be a keyword. And property certainly isn't a keyword, since you _can_ use it as an identifier, so it isn't a keyword with @ prepended on either. True, @property is treated as a special symbol by the compiler, and I don't expect that it really treats it like an attribute with the name property (which it will pretty much have to do if we ever get user-defined attributes), but definitely isn't a keyword, because it was never possible for it to be a valid identifier in the first place. - Jonathan M Davis
