Memory Efficient HashSet

[Edwin van Leeuwen via Digitalmars-d-learn]

On Tuesday, 8 March 2016 at 08:12:04 UTC, Nordlöw wrote:
> Has anybody put together a memory-efficient D-implementation of 
> a HashSet
>
> Something like
>
> sparse_hash_set<> contained in
>
> https://github.com/sparsehash/sparsehash
>
> but in D.

There is an implementation in:
code.dlang.org/packages/emsi_containers

But to be honest I got stuck trying to use it (copy constructor 
disabled), so I used this very minimal wrapper around associative 
array:

private struct HashSet(E) {
     // TODO switch to proper implementation (not using AA)
     bool put( E el )
     {
         if ( el in set )
             return false;
         set[el] = set.length;
         return true;
     }
     size_t[E] set;
}

(I only needed put, since I used it to check whether we already 
encountered a value before in a lazy/non sorted implementation of 
uniq)