Proposal: user defined attributes

[Steven Schveighoffer]

On Wed, 21 Mar 2012 17:10:06 -0400, Jacob Carlborg <doob at me.com> wrote:

> On 2012-03-21 19:32, Steven Schveighoffer wrote:
>
>> In my proposal, I specified that the annotation can be applied only to
>> module-level functions (normal or templated), and the result of those
>> functions is what gets saved. So with that capability, you should be
>> able to store any CTFE-evaluatable struct:
>>
>> @annotation auto makeAPoint() {Point2d p; return p;}
>>
>> @makeAPoint int x;
>
> Does "@makeAPoint int x;" expand to "Point2d p; return p;"?

What I envision is that @makeAPoint translates to the CTFE engine calling  
makeAPoint with no arguments.  This returns a Point2d default  
initialized.  That result is stored in the TypeInfo (or ModuleInfo) in the  
appropriate location for the 'x' member.

Then you can query this using runtime or compile-time functions later on,  
using the name "makeAPoint".

So in effect, you can use any struct or type that can be constructed at  
compile-time.  But it allows you to specify which types (and in which ways  
they can be constructed) can be used as annotations.  It also allows you  
to name the way that type is used.

It also could give you a way to use the same type for different  
annotations, discernible by name.

-Steve