Re: Incomplete types used with generics

[Jeremiah <jeremiah.breeden@gmail.com>]

On Monday, May 11, 2015 at 9:43:55 PM UTC-4, Randy Brukardt wrote:
> You missed at least 6 months of wrestling with various AdaCore people about 
> this feature, specifically over some proposed ACATS tests. (Most of the 
> tests showed lovely GNAT bug boxes.) They were trying very hard to find 
> reasons that the tests were illegal, because there was an problem with the 
> design of their implementation that made the tests very hard to implement. 
> They managed to uncover some language problems that will probably be fixed 
> someday, but in particular, everyone eventually agreed that the test using 
> limited with (CC51010) is correct (now). I've heard that they've fixed the 
> compiler so that test works, so you'll probably be able to get that to work 
> at some future point (but surely not with GNAT GPL 2014, which clearly 
> predates the fixes).
Well that's definitely stinky.  Thanks for the info on that.

> I suspect that you ran afoul of the fact that the freezing rules differ for 
> tagged incomplete vs. untagged incomplete types, but even if you fixed that 
> you'd still be very likely to run into problems with current GNAT versions 
> unless you are a GNAT PRO user and can get a wavefront.
I'm definitely a novice at Ada compared to most here, so I will ask:  which freezing rules did I mess up on there with Node2_Type?  I am familiar with how freezing works to some extent (I usually mess it up but am able to tell when I can't override a procedure/function or use one as a primitive like I intended).  I was trying hard to not to invoke freezing too early.  I did the incomplete declaration, the access to it (should be good there?), and then assuming the compiler could do it (which you indicated it couldn't) I passed it as an incomplete type to a package instantiation.  Is there a better way to do that?  

Keep in mind my (previously unspecified) goal is to have a type that uses a smart access type (that's the generic) to reference itself.  Basically a node type that uses a smart access type to handle the references (with a weak reference to the parent of course).

Thanks again!