Le 06/04/2012 11:41, Johannes Pfau a écrit :

Am Fri, 06 Apr 2012 00:48:34 -0700
schrieb Walter Bright<newshound2@digitalmars.com>:

On 4/6/2012 12:35 AM, Alex Rønne Petersen wrote:

It actually can be a problem. In .NET land, there are many
attributes across many projects (and even in the framework itself)
with the same names. It turns out that regular namespace lookup
rules alleviate this problem.

Perhaps a better scheme is:

    enum foo = 3;

    ...

    @attr(foo) int x;

That way, foo will follow all the usual rules.

The last time custom attributes where discussed, a C# like model was
proposed. Is there a good reason why we should deviate from the C#
implementation?

C#:
http://msdn.microsoft.com/en-US/library/48zeb25s(v=vs.80).aspx
http://msdn.microsoft.com/en-US/library/sw480ze8(v=vs.100).aspx
http://msdn.microsoft.com/en-US/library/z919e8tw(v=vs.80).aspx

(C# attributes can be applied to almost everything, therefore sometimes
 "disambiguating targets" is necessary. Probably not needed in D):
http://msdn.microsoft.com/en-US/library/b3787ac0(v=vs.80).aspx

Syntax in D would be different of course, but I see absolutely no need
for the redundant (and ugly) @attr.

Declaring a custom attribute:
---------
module std.something;

struct Author
{
    string name;
    public this(string name)
    {
        this.name = name;
    }
}
---------

Using it:
---------
import std.something; //Usual namespace lookup rules apply to attributes

/*
 * @Author(param) calls the constructor of the Author struct and
 * attaches the struct instance to test. Probably @Author (without
 * parenthesis) coud be made to mean std.something.Author.init
 */
@Author("Johannes Pfau") int test;
---------

Attaching attributes multiple times as in C# should be possible.

Using reflection to get that attribute:
---------
if(__traits(hasAttribute, test, std.something.Author))
{
    Author[] authors = __traits(getAttribute, test,
        std.something.Author);
}
---------

An array is used here to support attaching the same attribute multiple
times. Of course "auto authors = ..." should be usable here too.

That is a really nice proposal !