opCmp with structs

[Alex via Digitalmars-d-learn]

On Saturday, 7 November 2015 at 00:19:56 UTC, Ali Çehreli wrote:

> Continuing from your hint: So, opCmp works but it is sort() 
> that cannot move objects of ku around because of that immutable 
> variable.

So my general question is: why immutable variables shouldn't be 
able to be moved (inside an array)?

> There may be references to ku objects or its id members and 
> those references may be depending on the immutability of that 
> member. const and immutable members effectively make objects 
> unassignable. (const part is the same in C++.)

And this is also something unexpected: yes, there may be such 
references and they should stay valid of course. But why 
shouldn't be a concrete collection of such references be 
sortable? Why this should affect other references to the 
individual 'ku' objects?