Re: Annotations or custom attributes

[Andrei Alexandrescu]

On 3/9/12 2:56 AM, Manu wrote:
Does D have a nice way to add annotations or custom attributes to entities?
In Java/C# for example, it is common to annotate things with useful
compile time information. I'd like to be able to do that in D on occasion.

For instance, I'm serialising some struct/class using reflection to some
text format, but there are a couple of members in a particular class
that I don't want to be written.
A nice solution might be that I could annotate various members:
@DoNotSerialise int thing; ... or something along those lines, whatever
concept you want to apply, which I could then inspect in static if()
logic to produce some requested additional behaviour.

This is a trivial example, but looking at C#/Java, you can see how many
useful things can be done with this sort of system.
How would it be done currently?

I think a good approach in D would be to define mixins that work in 
conjunction with the feature involved, for example:

class A {
    int thing;
    mixin(DoNotSerialize!"thing");
    ...
}

or together:

class A {
    mixin(DoNotSerialize!(int, "thing"));
    ...
}


Andrei