Re: Suggestion: Allow functions returning abstract types in certain situations

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dan'l Miller" <optikos@verizon.net> writes:

> The size of an abstract type is not known in this situation.

The size of the abstract type is know from the (possibly private) record
or record extension.

>>     package Pack1 is
>>         type T1 is abstract tagged record ... end record;
>>         function Func (X : Integer) return T1;  -- not currently legal
>
> This whole topic seems to be going nowhere fast.  The size of T1's
> eventual concrete type (i.e., some member of T1'Class) cannot be known
> by Func (nor in general by callers of Func).  There could be many such
> eventual concrete types of T1; hence the insurmountable question will
> always be: which member of T1'Class was instantiated concretely?

No, no, I think you are misunderstanding the suggested language change.
Func is returning a T1, whose size is perfectly well known to the
compiler.  It's not returning some other member of T1'Class.

Anyway, this:

  function Class_Wide_Func (X : Integer) return T1'Class;  -- currently legal

IS legal, and it CAN return an object whose tag is anything
in the class.  The size in this case is determined at the
"return" in the body.

- Bob