Mutable class reference to immutable class

[Lodovico Giaretta via Digitalmars-d-learn]

On Saturday, 10 September 2016 at 19:46:51 UTC, Jonathan Marler 
wrote:
> This is been bugging me for a while. Is it possible to have a 
> mutable reference to an immutable class?  [...]

You are probably looking for std.typecons.Rebindable: 
https://dlang.org/phobos/std_typecons.html#.Rebindable