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Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
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Date: Mon, 18 Jul 2005 23:51:12 -0400
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Date: 2005-07-18T23:51:12-04:00
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Matthew Heaney wrote:
> 
.......
 > Does not exist in the Ada 2005 standard container library.
.......
 > Does not exist in the Ada 2005 standard container library.
.......
> 
>>And for proofs it is essential that the premises were correct. Programming
>>is not much different...
> 
> 
> Yes, that's called a "reference manual."
> 

And we are talking about Holy scripture ;)

> 
> Of course a container must "mix implementation and interface," since it
> has to provide access to its elements.  The essential container design
> problem is doing that without exposing representation details.  Cursors
> are that mechanism.
> 

This "must" is too strong. Some libraries use access types and don't 
"mix implementation and interface." If Ada.Containers exposes 
representation details (Cursors) i.e. "mixes implementation and 
interface," then it is not the essential container design then?

> There's nothing bad about this; it's simply the nature of a container

There is nothing bad about this, but it's not the nature of a container 
abstraction; it's a nature of your specific vision of a container 
abstraction.

> abstraction.  The container should get out of the way as much as
> possible, since it's the elements we care about.
> 

Yes, and Cursors are probably a part of this "as much as possible".

> 
> 
>>[and again, sets could be searchable and not]
> 
> 
> The sets in the Ada 2005 standard container library are searchable.

Then it is not the common set abstraction. In the common set abstraction 
search degenerates into membership test and the common set abstraction 
contains no such things like First, Last and Cursor.