Re: Question on Ada 9X vs Ada 83.

[olivea!news.bu.edu!inmet!spock!stt@uunet.uu.net (Tucker Taft)]

In article <CDrDrJ.4px@News.MR.Net> info@xinotech.com (Brian Hanson) writes:

>I have a question about a compability issue and wonder if anyone on the
>net
>knows the answer or knows whom I could direct my question.
>
>The issue is "Derived type inherits all operations of Parent".
>
>An example is
>
>  package P is
>    type Some_Array is array (1 .. 10) of Integer;
>    function "&" (Left, Right: Some_Array) return Some_Array;
>    type New_Array is new Some_Array;
>  end P;
>
>I understand that in Ada 9X, New_Array inherits "&" from Some_Array and
>that does not happen in Ada 83.
>
>The my questions are:
>  1 - Would this happen if these declarations were in a procedure body?

Yes.  When a primitive operation is overridden, the overriding operation
becomes primitive as well, and is hence available for being inherited
on (subsequent) derivation (see RM9X-3.2.3(2);3.0/4.0 last sentence).

>  2 - If the function declaration was moved after the type declaration
>for
>      New_Array would New_Array still inherit the "&" function from 
>      Some_Array?

No, a type only inherits primitive operations that are visible
at the point of the derivation (RM9X-3.4(16);3.0/4.0).  So New_Array
would inherit the predefined "&" instead of the user-defined one
if the user-defined "&" were declared after the point of derivation.

>I have tried to figure this out by reading the Ada 9X RM but it was not
>very clear to me.

I hope the above citations help.

>Brian Hanson

S. Tucker Taft    stt@inmet.com
Ada 9X Mapping/Revision Team
Intermetrics, Inc.
Cambridge, MA  02138