Self-referential struct mixins

[rbscott]

Hello,

I recently started using D, and I am exploring some of the 
functionality in CTFE. I ran into a case that I can't get past. 
The goal is to take a JSON API Schema and convert it into D types 
using CTFE. The problem is, the types can be self-referential.

A simplified form of the language would look like:

{ "A" : { "type": struct, "fields" : { "b": { "type": "string" }, 
"a" : { "type": "A" }}}

This would yield a type "A" that has two fields, "a" and "b". 
Where "a" is a string and "b" is of type "A". Or in D:

struct A {
   string b;
   A* a;
}

This is a simplified example, but imagine this is highly nested 
to generate arbitrarily complex types that could reference on one 
another.

I got this working in the simple case if none of the fields are 
self-referential, but it breaks as soon as there is a loop.

Here is a gist which demonstrates the issue: 
https://gist.github.com/rbscott/ee0f3ba94296f9c8224a8c4c13c2f026.

I think I can workaround this by with string mixins everywhere, 
but the structure generation logic is complex enough that I would 
prefer not to do that. This approach could be totally off, so any 
suggestions would be greatly appreciated!

thanks,
rbscott