Member is @disable this(this), parent uncopyable

[James Blachly]

I have a struct S with member containers.UnrolledList [1]. UnrolledList 
is @disable this(this), but this unfortunately makes my struct S also 
un-copyable, which now breaks some of my debugging statements which rely 
on toString, as writeln, format, etc. all copy the object. This leaves 
me in the unfortunate situation that my release builds work, but debug 
builds do not.

First, how do we deal with toString, std.format, writeln, etc. with 
un-copyable objects, when it is only a member that is uncopyable?  In my 
case I got around this by creating a pointer and moving the 
initialization to the constructor, but I wonder if there are other ways?

Second, why  must an object in its entirety be copy-able for these 
functions to call toString() ?

Finally, the error message gave no clue that it was a member 
(UnrolledList in my case) that was @disable 'd and it took some digging 
back through several commits to figure out what was happening -- how 
could we improve the error messaging?

Thanks as always in advance

[1] https://github.com/dlang-community/containers