Inability to dup/~ for const arrays of class objects

[Ali Çehreli]

On 05/28/2013 04:32 PM, Peter Williams wrote:

 > I find that dup works for const T[] when T is not a class (although I
 > haven't tried it with pointers).  This means I write two versions of my
 > code - one for classes (which does (cast(T[])).dup) and one for the rest.

There is current and related thread on the D.learn forum:

   http://forum.dlang.org/post/bsbhpdgcpfmkvsclsskq@forum.dlang.org

I think it is unnecessarily restrictive that a const class variable 
cannot refer to another class object:

class C
{}

void main()
{
     const(C) c;
     c = new const(C);    // <-- compilation error
}

I think this limitation is at the core of your issue as well: .dup 
creates mutable objects but your array is not able to contain const 
class variables to refer to those mutable objects. I think it should be 
possible.

I have a feeling that this may be related to that surprising issue with 
C and C++:

   http://www.parashift.com/c++-faq-lite/constptrptr-conversion.html

The reason I suspect so is because a class variable is one level of 
indirection and a slice is another level of indirection. Does that make 
this issue the same as the C++ issue? If not, perhaps the implementation 
of such a limitation is the cause of this bug. (?)

Ali