Can attributes trigger functionality?

[Moritz Maxeiner via Digitalmars-d-learn]

On Wednesday, 6 September 2017 at 02:43:20 UTC, Psychological 
Cleanup wrote:
>
> I'm having to create a lot of boiler plate code that creates 
> "events" and corresponding properties(getter and setter).
>
> I'm curious if I can simplify this without a string mixin.
>
> If I create my own attribute like
>
> @Event double foo();
>
> and I write any code that will trigger when the event is used 
> and add more code(such as the setter property and events that I 
> need?
>
> Obviously I could write some master template that scans 
> everything, but that seems to be far too much over kill. A 
> string mixin is probably my only option but is a bit ulgy for 
> me.
>
> Since attributes can be defined by structures it seems natural 
> that we could put functionality in them that are triggered when 
> used but I'm unsure if D has such capabilities.
>
> Thanks.

User defined attributes (UDAs) are in and of themselves only 
(compile time) introspectable decoration [1] (they only carry 
information). If you want to trigger specific behaviour for 
things that are attributed with a UDA you indeed need to some 
custom written active component that introspects using 
`__traits(getAttributes, symbol) and generates injects generates 
the behaviour (e.g. using a string mixin as you noted).

[1] https://dlang.org/spec/attribute.html#UserDefinedAttribute