Re: Making sense of predicates

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:9vlzla1igu9w$.1ifys2xkaugrn$.dlg@40tude.net...
> On Mon, 21 Oct 2013 23:35:59 -0500, Randy Brukardt wrote:
>
>> It should be one step (only). We'd need something like co-derivation for
>> that, which might make sense to pursue someday (the main reason would be 
>> to
>> get rid of access types altogether, but to do that you need some sort of
>> handle, like the container cursor -- and clearly you need to be able to
>> derive the container and its handle together). But that would be a big 
>> job
>> to define properly, it would take the existing inheritance rules and make
>> them much more complex. (There are already 3 pages of rules associated 
>> with
>> inheritance for derived types.)
>
> It is not only access types. It is relationships between types: Pointer -
> Target, Array - Index - Element, etc.

Yes, of course. The idea is that you'd be able to declare any set of types 
as "co-tagged" or something like that. (I'm thinking on the fly here, so 
don't read anything much into the names.) Then they'd have to be derived 
(extended) together as a group.

> If you try, as Ada designers keep on doing, to handle that at the language
> level for each built-in type individually, you indeed end up with 
> something
> as horrific as accessibility rules are. That does not work.

That's doesn't remotely resemble what I was thinking of; I was only thinking 
about a new kind of derivation and possibly a new kind of tagged type. Basic 
building blocks, nothing "built-in".

                                  Randy.