Re: Please explain why this is wrong...

[jimr@col.hp.com (Jim Rogers)]

Robert Dewar (dewar@cs.nyu.edu) wrote:
: Your program is clearly wrong, and the message from GNAT is quite precise.

Yes, you are correct.  I have learned, thanks to the kind expalnations from
Mssrs Dewar and Nebbe, esxactly how my thinking erred.

: You have a primitive operation New_Square, which is inherited when you
: make a rectangle to give a function New_Square that returns a Rectangle.

This is precisely what I overlooked.  I was attempting to translate a
rather trivial C++ inheritence example into Ada.  I ignored (and was
ignorant of) the inherited constructor.

:............
: If as I suspect, you really did not intend New_Square to be inherited, but
: rather intended it to serve as a constructor only for the Square case, then
: you must be sure that you do not declare in as being primitive. The easiest
: way to declare non-primitive operations is to nest them in a subpackages;

:    package Constructors is
:       function New_Square .. return Square;
:    end Constructors;

This solution was so simple and obvious that I would probably have missed it
for quite a while.  As you have already guessed, I am sure, I am not 
exactly an Ada wizard....yet.

I hope this thread has served as a good example of the problems explained by
Tucker Taft concerning Ada constructors in this same news group.

Thank you all.  I have learned yet again why I prefer Ada to C++.

--
------------------------------------------------------------------------------
| Jim Rogers                    | Dead Reckoning:                            |
| Hewlett-Packard Company       | Traditional form of rough-estimate         |
| Colorado Springs Division     | navigation used for hundreds of years by   |
|                               | sailors, almost all of whom are dead.      |
| jimr@col.hp.com               |                                            |
------------------------------------------------------------------------------