How to use sets in D?

[mark]

I am porting code from other languages to D as part of learning 
D, and I find I've used sets quite a lot. AFAIK D doesn't have a 
built-in set type or one in the std. lib.

However, I've been perfectly successfully using int[E] where E is 
my ElementType, and adding with set[element] = 0. I mostly only 
need add, remove, iteration, and in, with uniqueness what I care 
most about.

I know I could use bool[E] and set[element] = false, or I suppose 
container.rbtree. Would either of these--or something else 
built-in or in the std. lib.--be better?