Re: GCC 4.0 Ada.Containers Cursor danger.

[Georg Bauhaus <bauhaus@futureapps.de>]

Dmitry A. Kazakov wrote:

>>  B := {x: x in A | x >= 0};
>>
> See the well-ordering theorem and then the axiom of choice. (:-))

Yes, therefore Ada.Containers can't be contradicting basic
mathematics that much. :-)


> Think about differences between:
> 
> - An unordered set of unordered elements
> - An unordered set of ordered elements
> - An ordered set of unordered elements
> - An ordered set of ordered elements (and these orders are different)

Can we resolve the name overloading by using
"as if physically positioned" and
"accessible in sort order", respectively, for the moment?
Then there may or may not be an overlap between the two orders in practice.
An implementation may choose to physically position
the elements in sort order in an internal structure, or not.


>>For me, First and Last (or whatever you call them) *do* make sense
>>for any reasonable notion of a set in programming, sorted or not,
>>even when used in computer science.
> 
> 
> Hmm, what about ring buffers?

You don't mean the two pointers in a ring buffer cannot
make sense?


>>I find Cursors useful when I want to put an index set into operations
>>inside a computer. When I'm can use any container,
>>how could I implement index sets without Cursors?
> 
> 
> You are mixing implementation and interface.

How can I think about "putting into operations" with just interfaces?
(In any practical sense of operation inside a computer.)
So how can I implement index sets without Cursors?


>>Find is a membership test, how could it not make sense for
>>a set?
> 
> 
> No. Find is more general.

(It is still also a membership test.)


> [and again, sets could be searchable and not]


What do you mean by a set container that is used in a program
and that you cannot search? You can't find members, so how
is a set that you cannot search more useful than one in which
you can actually find an element?