On 2012-11-06 15:23, Gor Gyolchanyan wrote:
What if the data in the attribute needs to be specific to the symbol on which the attribute is set on? Can you query the symbol from inside the attribute? What if the attribute needs to change the symbol being defined? For instance (using commonly desired syntax):@flags enum A { ... } the "flags" attribute would replace the declaraction of A with another enum declaration with the same name and same members, but with replaced initialization and would static assert(false, "flags enum can't have initializers") if any initializers are given. The existing "[data] declaration" is one thing. It adds compile-time data to symbols, which is very very important, but it's not the only thing that is needed. What I described above is not quite an attribute, but an annotation. The semantics of attributes as Walter made them is perfect. The annotation should be defined like so: template myAnnotation(alias symbol, annot_args...) { // ... ["myAnnoration adds this attribute"] alias symbol myAnnotation; // or alias anything else if a change in necessary. } @myAnnotation(arg1, arg2, arg3) class Declaration { } here the "symbol" is passed to the template as the first parameter and the parameters in the parentheses are passes after it. It's basically a thin syntactic sugar over some manual (and very ugly) manual template instantiations (and mixins), so it doesn't add anything new. Annotations then become a way to statically replace declarations. This would be perfect to replace Scoped!MyClass mc; with: @scoped MyClass mc; Which looks quite like a very beautiful built-in syntax, but is actually a library solution. IMHO, Attributes as they are should stay, but annotations should be added. P.S. Thank you, Walter very very much for making attributes!!! :-)
I like this proposal as well. -- /Jacob Carlborg
