Source code annotations alla Java

[Steven Schveighoffer]

On Thu, 20 Jan 2011 15:03:55 -0500, Jacob Carlborg <doob at me.com> wrote:

> On 2011-01-20 19:18, Steven Schveighoffer wrote:
>> On Thu, 20 Jan 2011 13:07:58 -0500, Jacob Carlborg <doob at me.com> wrote:
>>
>>> On 2011-01-20 15:02, Steven Schveighoffer wrote:
>>>> On Thu, 20 Jan 2011 08:47:28 -0500, Justin Johansson <jj at 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;

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