Proposal: user defined attributes

[Adam D. Ruppe]

Another argument against would be "can we do
this in the language today?"

And the answer is "sort of, but not really":

void a(@note(...) int arg) {}


You could perhaps do something like:

void a(int arg) {}
mixin("enum " ~ a.mangleof ~ "_arg = " ~ ...);

and then get the listing by looking at allMembers
and comparing the name... but, it gets messy
fast - the attribute is somewhat far from the declaration,
so I betcha it will get out of sync.


Getting the attribute on param 0 too would consist
of using stringof tricks to get the name, then mixing
it in to get that variable.


This isn't a proper tuple either - more care would be
needed to handle multiple notes.



So, you could make it work, but it is hideous, fragile,
and probably less useful even if you look past that.

I've seen some nice implementations of struct level annotations,
using mixin templates, but the killer feature for me, personally,
is putting it on function parameters as well.


I think the language addition (which breaks nothing existing
today; it is purely additive) is necessary to get something
generally useful, not just useful in a few cases.