Checking all elements are unique.

[Dorian Haglund via Digitalmars-d-learn]

Hello,

I have an array of objects of class C which contain a id member.
I want to figure out if all the id members are unique using 
functional primitives.

For example, if I have:

class C
{
   int id;
}

and an array of C 'Cs';

My idea was to do:

auto ids = Cs.map!(c => c.id);
assert(equal(ids.sort().uniq(), ids.sort()));

But it doesn't compile because I can't can call sort on ids.

Any idea why ? and how to solve my initial problem, which is to 
check all ids are unique.

Regards,

Dorian