sorting associative array's keys by values

[maarten van damme]

Ok, everything worked (nearly perfect). Sometimes the webpage gets
completely messed up  ("<" changes to d134 or something like that) but
the tests handle it rather well.
That's why I decided to improve it a bit and use treads. I've always
been afraid of d treads because I never really got the grasp of that
message passing system but hey, there is a first time for everything.
Maybe I was a bit optimistic as I now already run into troubles.

I have two arrays of the form
int[string]

To pass them from the spawned function back to the spawner I wanted to use
tid.send( array1,array2);

This was illegal, they have to be either immutable or shared. I've
read somwhere that D tries to avoid shared where possible (with that
message passing system) so I went for immutable and changed it over to
tid.send(cast(immutable(int[string]))array1,...) (you get the idea)

Not only does this look ugly, it's looks like what I'm doing isn't
really correct.
But anyway, onto the next part, receiving it.

I used
auto msg=receiveOnly!(int[string],int[string]);

of course this fails because I send immutable items and want to receive mutables
I then changed it to
auto msg=receiveOnly!(immutable int[string],immutable int[string]);

Compilation now fails with the very informative
C:\D\dmd2\windows\bin\..\..\src\phobos\std\concurrency.d(612): Error: can only i
nitialize const member _field_field_0 inside constructor
C:\D\dmd2\windows\bin\..\..\src\phobos\std\concurrency.d(612): Error: can only i
nitialize const member _field_field_1 inside constructor

Why is treading made so damn hard?
what have I done wrong now?