How to make AA key a pointer

[Clinton]

Hi all, I need advice from better developers on this concern.

I'm using an AA to reference another array for quicker access:

[code]
alias contactId = string;
bool[contactId][] matches;
ulong[contactId] idsToMatches;

bool[string] matchesForId(string id) {
   return matches.get(idsToMatches[id], bool[string].init);
}
[/code]

Just wondering, how do I set the keys to avoid copying the id 
string? So, let's say ids come from another array of structs(e.g. 
Contact[]). I want to avoid having two copies of the string id 
value in both of these AAs above (to avoid using extra memory 
usage).

The reason this is a potential issue is because these arrays can 
get extremely large. This is to match duplicate contacts and 
group them in matches. The reason I use bool is because it's the 
smallest size type and I don't think I can use void.

I guess my question is: does dmd already create pointers to the 
id from the AA, or is each new key a new allocation?