Inability to dup/~ for const arrays of class objects

[Steven Schveighoffer]

On Tue, 28 May 2013 22:20:08 -0400, Jonathan M Davis <jmdavisProg at gmx.com>  
wrote:

> On Tuesday, May 28, 2013 20:37:12 Steven Schveighoffer wrote:
>> This is a different problem. Your problem is you can't apply const
>> selectively to the tail of the reference. It's fundamentally sound, but  
>> D
>> lacks the syntax to do it.
>
> The syntax is actually the easy part. The problem is that the type system
> itself doesn't differentiate between a class and a reference to a class,  
> and
> the whole compiler is wired that way. So, while adding a new syntax  
> isn't that
> hard (several have been proposed before), actually implementing it is a  
> royal
> pain (enough so that Walter gave up on it). It would definitely be nice  
> to have
> that fixed though.

No, this is wrong.  The issue is entirely syntax.  And it is hard, because  
*conceptually*, it's difficult to separate out the reference from the  
data.  It's hard to say "The part of C that isn't the reference" in a  
succinct way.

Michel Fortin has created a pull request to make

const(T)ref

work, and only apply the const to the data.  It's certainly doable.  But  
the syntax, as you can see, is ugly.

As it turns out, we need more than this, and a more critical problem to  
solve is creating tail-const custom ranges (I am working on an article to  
discuss and hopefully address this).

-Steve