Am Fri, 06 Apr 2012 00:48:34 -0700 schrieb Walter Bright <newshou...@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.
