Re: Q: access to subprogram

[dewar@cs.nyu.edu (Robert Dewar)]

"While the lack of direct support for recursive types across package
boundaries and lack of assertions are more important (IMO) goofs, and
while the evinced reasons for the latter one are mind numbingly
incomprehensible, this latest example would appear to take the crown
for the most stupefying goof."

One interesting question to ask is how people are using Unrestricted_Access
in GNAT. During the discussion of this issue in WG9, we did have some
examples that purported to show the importance of this issue (I am
including Bill Taylor's discussion of iterators), but they were 
unconvincing, since there seemed to be alternative expressions that
were quite acceptable (the final vote on this issue was unanimous
by delegations as I remember, which means there was no strong advocate
for keeping the feature -- there certainly were some energetic arguments
over an extended period of time -- but by the end, everyone was convinced.

Now the difficulty with arguing by example is that of course you don't know
if you have found the critical examples or not. Note that the entertaining
thing about Jon labeling this as a stupefuing goof is that in the message
*just* before this one, he declared that real programs have no nesting
anyway, and of course all this business about closures is irrelevant
nonsense in programs that don't have any nesting!

So, the intersting question is: are there examples that people are
running into, involving nesting of course, since otherwise the issue
does not arise, where the use of Unrestricted_Access in GNAT seems
really critical. I must say I implemented this attribute because it
fell out literally free to do so (the real thing I needed was an access
attribute that did not require aliased, but the procedure case just
fell out), not because I had a critical use in mind, but I certainly
have found some uses for it, none that I would label as critical.

But if someone can present some really nice example where the use of
Unrestricted_Access is critical, that would be interesting.