I have a question regarding using a struct value as user-defined attribute. The use-case I am trying to get working is as follows:

struct message {
    int atom;
}

...

class AnActor : ... {
    @message(id) void myHandler(string arg1, real arg2) {
    }

    mixin ... // a mixin that builds message dispatch
}


The 'message' attribute defines methods of the class that will participate in message dispatch argument matching. This works fine but I want to take this one step further. I want to be able to give a message and a handler an ID that more strictly directs a message (and gives an error if arguments does not match).

The problem I have is quite simple - getting the value of 'atom' out of the message attribute. How can I do this? I did not post any of my actual code, I hope the above example describes the problem.

Regards,
Ulf

On Tuesday, 16 April 2013 at 06:29:22 UTC, Ulf Johansson wrote:
> I have a question regarding using a struct value as user-defined attribute. The use-case I am trying to get working is as follows:
>
> struct message {
>     int atom;
> }
>
> ...
>
> class AnActor : ... {
>     @message(id) void myHandler(string arg1, real arg2) {
>     }
>
>     mixin ... // a mixin that builds message dispatch
> }
>
>
> The 'message' attribute defines methods of the class that will participate in message dispatch argument matching. This works fine but I want to take this one step further. I want to be able to give a message and a handler an ID that more strictly directs a message (and gives an error if arguments does not match).
>
> The problem I have is quite simple - getting the value of 'atom' out of the message attribute. How can I do this? I did not post any of my actual code, I hope the above example describes the problem.
>
> Regards,
> Ulf

foreach(attribute, __traits(getAttributes, AnActor))
{
    static if (is(typeof(attribute) == message))
        pragma(msg, attribute.atom);
}

On 2013-04-16 08:29, Ulf Johansson wrote:
> I have a question regarding using a struct value as user-defined
> attribute. The use-case I am trying to get working is as follows:
>
> struct message {
>      int atom;
> }
>
> ...
>
> class AnActor : ... {
>      @message(id) void myHandler(string arg1, real arg2) {
>      }
>
>      mixin ... // a mixin that builds message dispatch
> }
>
>
> The 'message' attribute defines methods of the class that will
> participate in message dispatch argument matching. This works fine but I
> want to take this one step further. I want to be able to give a message
> and a handler an ID that more strictly directs a message (and gives an
> error if arguments does not match).
>
> The problem I have is quite simple - getting the value of 'atom' out of
> the message attribute. How can I do this? I did not post any of my
> actual code, I hope the above example describes the problem.
>
> Regards,
> Ulf

Use __traits(getAttributes, symbol) to get the attributes out of the given symbol. It will return a tuple with the attributes.

I would guess it would look something like this:

message msg = __traits(getAttributes, AnActor.myHandler)[0];
int atom = msg.atom;

See the docs:

http://dlang.org/traits.html#getAttributes
http://dlang.org/attribute.html#uda

-- 
/Jacob Carlborg

On 04/16/2013 08:29 AM, Ulf Johansson wrote:
> ...
>
> The problem I have is quite simple - getting the value of 'atom' out of
> the message attribute. How can I do this? I did not post any of my
> actual code, I hope the above example describes the problem.
> ...


struct message{
    int atom;
}

class AnActor{
    @message(3) void myHandler(string arg1, real arg2){ }
    static assert(__traits(getAttributes, myHandler)[0].atom==3);
}

(Consider posting to d.D.learn for basic questions.)

On Tuesday, 16 April 2013 at 06:29:22 UTC, Ulf Johansson wrote:
> I have a question regarding using a struct value as user-defined attribute. The use-case I am trying to get working is as follows:
>
> struct message {
>     int atom;
> }
>
> ...
>
> class AnActor : ... {
>     @message(id) void myHandler(string arg1, real arg2) {
>     }
>
>     mixin ... // a mixin that builds message dispatch
> }
>
>
> The 'message' attribute defines methods of the class that will participate in message dispatch argument matching. This works fine but I want to take this one step further. I want to be able to give a message and a handler an ID that more strictly directs a message (and gives an error if arguments does not match).
>
> The problem I have is quite simple - getting the value of 'atom' out of the message attribute. How can I do this? I did not post any of my actual code, I hope the above example describes the problem.
>
> Regards,
> Ulf

Thanks, I have it working now! I was getting some strange errors and I guess I needed to know that it could be done. I will use the learn forum next time :)