Re: Question about tagged types and functions

[jsa@organon.com (Jon S Anthony)]

In article <4nvhdo$ri7@ns.interserf.net> dhunter@interserf.net (David Hunter) writes:

> situation in which you end up with "derived_object := parent_object"
> but doesn't Ada-95 forbid that anyway?  I mean, you couldn't do
> 
> 	d : DerivedType;
> 	b : BaseType;
> 	d := b;
> 
> so the error "d := Create;" would be caught by the type
> rules anyway, right?

This is pretty much why the error is being flagged the way it is.  If
you assume that the current rule was not there and you did not have to
override, then a new Create with result type DerivedType is implicitly
declared _immediately_ after the declaration of DerivedType.  So, the
case you site:

    d := Create;

would not have any type error at all.  But, the actual Create bound
here would be the Create with result type BaseType with an implicit
conversion on the resulting object _away_ from the root of BaseType
to DerivedType.  Ba-Boom!  See 3.4(17-23, 27) and 3.9.2(20).

/Jon

-- 
Jon Anthony
Organon Motives, Inc.
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Belmont, MA 02178

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