Re: class wide iterable (and indexable)

[George Shapovalov <gshapovalov@gmail.com>]

Original poster here.
I think I did it again - that is broke gnat again. 

But first a small update: I have cleaned up and systematized the original code somewhat and added the description. Plus I added the complete "demo" code of the basic mix-in situations. No proper description yet though. The general idea is to create a small depository of common composition situations, to have some base tested code that can be expanded upon.. Two sample compositions are implemented in the code already: the basic mix-ins and the "list interface" over which Ada.Containers.Vectors.Vector can be directly overlayed (among other implementations).
The link to the project is here:
https://github.com/gerr135/ada_composition
(renamed from original ada_gems to avoid name clash with existing Ada Gems by AdaCore).

In trying to expand on that last example - the indexable/iterable and overlayable by existing type interface, I have stumbled upon a rather weird behavior of compiled code. The expansion deals with trying to tie a type hierarchy to the hierarchy of list implementations - not to have a single generic type at the top and children units using the same. Instead this code has a generic interface at the top, and children take specific types implementing interface at the top. This works fine (with minimal code changes in the "library" itself from the previous case) for the basic composition types (record encapsulating wither array of ACV.Vector). But when I try to pass ACV.Vector overlais directly over interface as a generic parameter, it seems the compiler gets confused. While passing the constructed Vector into the List object it raises run-time exception:
raised PROGRAM_ERROR : adjust/finalize raised STORAGE_ERROR: System.Memory.Alloc: heap exhausted

which is rather weird in itself. What's more, a simple whitespace change - splitting the line of code directly above into two (inserting line break between two trivial TEXT_IO ops that are in the same line in the code) changes that error into:
raised PROGRAM_ERROR : adjust/finalize raised STORAGE_ERROR: stack overflow or erroneous memory access

The line of code in question is this:
ld(i) := Base_Interface'Class(set_idx_vector(i));

the setter runs fine (and identical setter for a differently composed version of the base type completes fine *and* allows the constructed object to be passed), but attempt to assign the constructed object to the List container blows up with that STORAGE_ERROR. Please note: only the last variant is affected, that is List composition directly overlaying ACV.Vector over List_Interface, *but not* a more common encapsulation having ACV.Vector a record entry.

Unfortunately. as before, I cannot post just a line or two of code that would reproduce the entire situation. Providing indexing and iteration for the entire type hierarchy takes some code. Please see this specific link for the appropriate part:
https://github.com/gerr135/ada_composition/tree/master/list_combo

This *is* the minimal code that reproduces the situation as far as I can tell..

I cannot see why this specific variant would be "wrong" in some way - the overal interface is the same for all 3 variants. Plus that weird behavior (sensitivity to whitespace) makes me suspect some problem with gnat here. But maybe I overlooked something.
Any ideas are appreciated. 
Thank you!