proper way to find if attribute present?

[Dicebot]

I use this small helper in vibe.d:

=======================
template extractUda(UDA, alias Symbol)
{
     import std.typetuple : TypeTuple;

     private alias TypeTuple!(__traits(getAttributes, Symbol)) 
udaTuple;

     private template extract(list...)
     {
         static if (!list.length)
             enum extract = null;
         else {
             static assert (!is(list[0] == UDA), "extractUda is 
designed to look up values, not types");

             static if (is(typeof(list[0]) == UDA))
                 enum extract = list[0];
             else
                 enum extract = extract!(list[1..$]);
         }
     }

     enum extractUda = extract!udaTuple;
}
=======================

Used like this:
=======================
@Bar("value") void foo();

enum uda = extractUda!(Bar, foo);

static if (is(typeof(uda) != typeof(null)))
     static assert (uda == Bar("value"));
=======================

It is far from perfection but can serve as a starting point for 
more complete implementation (though I have kept certain 
limitations intentionally)