Re: How to get Ada to ?cross the chasm??

[Paul Rubin <no.email@nospam.invalid>]

"Randy Brukardt" <randy@rrsoftware.com> writes:
> All of the Ada containers have "cursors", which serve the reference 
> function. You need something like that to specify where to insert something 
> in a tree ("insert_child (tree, parent)" - the parent is represented by a 
> cursor).

Ok, but can you insert the same child tree into multiple places in the
parent?  If yes, what happens if you insert it in 5 places, then delete
3 of them, then insert a few more, then delete some of those?  Is there
reference counting, or are you supposed to do it manually?  If manually,
why would you choose to use such a system if you had an automatic one
available?

What if you want one of the elements of a tree node to be a pointer to
its parent?  That's very common in (say) expression trees in compilers,
which you work on, or similarly in XML DOM objects or the like.  So
that's a natural source of circular structure in data.  In that case,
reference counting can fail because if you delete a node, its subtrees
can become unreachable while still containing references.  GC is a
completely normal way to handle this.

> Depends on the job, of course. Much of my software indeed works that way, 
> because there is much less security issues with compiled-in settings.

There is something to be said for that, but I've still been taught that
a principle of configuration management (CM) is to keep stuff like
compilers away from the system as much as you can, so who knows.  In the
case of the corporate jargon generator though, I'd consider the phrase
lists to be data rather than settings.  So having them compiled into the
program still seems awfully primitive.