Re: New, and don't understand the error message!

["Pat Rogers" <progers@classwide.com>]

"Danny Woolston" <dannywooly@yahoo.co.uk> wrote in message
news:d17ba8b2.0205151034.6f1d1961@posting.google.com...
<snip>
> linked_lists_test.adb: Error: line 6 col 57 LRM:3.9.1(3), The
> accessibility level of a record extension shall not exceed that of its
> parent; this also applies in a generic instantiation
>        (In instance of generic Linked_Lists at linked_lists.ads: line 40 col
10)

In effect the compiler is telling you that a new type (ie, the "record
extension") derived from an existing tagged type (the "parent") cannot be
declared at a more deeply nested level than that of the "parent" type.  For
example, a tagged type declared in a library package can only have extensions
also declared at the library level.  ("Nesting" isn't quite the proper term for
"accessibility level", but it will be close enough to get the idea across.)

The gist of the rationale for the rule is that it precludes any attempt to
dispatch to routines that no longer exist.

Have a look at a good textbook; the error message above is exactly right in what
it is telling you, but the terms it uses are precise and must be understood in
order to know what to do.  (Reading the RM is probably not the best way to
start.)  It is a subtle topic and the textbook will/should explain it at
sufficient length.

---
Patrick Rogers                       Consulting and Training in:
http://www.classwide.com          Real-Time/OO Languages
progers@classwide.com               Hard Deadline Schedulability Analysis
(281)648-3165                                 Software Fault Tolerance