const(X) member of Y

[Dan]

Start with:

struct X {
   char c[];
}

Assume you want value semantics - postblit provides this 
capability. It appears with 2.061 'this(this) const' is now 
supported. Previously, only 'this(this)' was recognized (i.e. 
called) when expected. To get value semantics a developer must 
choose between these two and for this case the goal is to ensure 
'c = c.dup;' so value semantics are preserved.

Case 1: Go with 'this(this) { c = c.dup; }'. This works just fine 
except for the case where you want a const(X) as a member of some 
other class. For example: struct Y { const(X) x; }.

Case 2: Go with 'this(this) const { c = c.dup; }'. This is not 
possible because you can not change 'c' since the function is 
const. Maxim Fomin pointed out a workaround.

struct X {
   char c[];
   void _postblit_() { c = c.dup; }
   this(this) const {
     void delegate() dg = &_postblit_;
     dg();
   }
}

This workaround succeeds, but, based on this thread 
(http://forum.dlang.org/thread/ywispsasaylqscyuayae@forum.dlang.org) 
I don't know if it is a bug or not. If it is not a bug, I would 
doubt it is the prescribed approach for doing this?

So, the question is:
What is the best *current* way to code X to achieve struct Y { 
const(X) x; } and what is the long run solution to this(this)?

Thanks,
Dan