Could use some help with porting problems

[Daniel Murphy]

It seems the problem you've run into is that a class reference cannot be 
tail-const.

Pointers can be tail-const like this:
const(Data)*
but there is no way currently (there are proposals) to make only the data 
and not the reference const.

A workaround is to use Rebindable in std.typecons.

An array of references to const classes becomes:
(Rebindable!const(Class))[]