The future of UDAs.

[Walter Bright]

On 11/28/2012 3:59 AM, David Nadlinger wrote:
> On Tuesday, 27 November 2012 at 15:49:45 UTC, Gor Gyolchanyan wrote:
>> Can you implement this use case?
>> Have classes mix in something,, which will register them in a single
>> place,
>> which can later suppl the registered classes as a type tuple.
>
> This is fundamentally impossible in the D module system if the "single
> place" S does not import the modules where the types are defined. Even
> if you could append strings to a "compile-time global" in S, this still
> wouldn't help you in any way because if you tried to mix in the string
> in S, you'd get nothing but a slew of undefined symbol errors.
>
> Maybe you can describe your use case a bit? I'm optimistic that there is
> a solution which is not radically incompatible with the design of D.
>
> David

In general, D even tries to avoid the concept of a "global". Modules are 
supposed to be unknown (and unknowable) unless they are imported 
(directly or transitively).

However, modules can self-register their contents to some imported 
"registry" via code in their static constructor.

I do not think this is a burden, because UDAs cannot be externally 
applied to an import. A module must be editted and the UDAs specifically 
added to them, so adding some boilerplate to the static constructor 
should not be an issue.