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Newsgroups: comp.lang.ada
Date: Mon, 29 Jul 2013 13:54:40 -0700 (PDT)
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Subject: Private function w/ Tagged return-type.
From: Shark8 <onewingedshark@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:16601
Date: 2013-07-29T13:54:40-07:00
List-Id: <comp.lang.ada>

Given the following:

with Ada.Streams;
package example is
    Type Subject is tagged private;
    function Create return Subject;
private
        function Input(
		    Stream : not null access Ada.Streams.Root_Stream_Type'Class)
	return  Subject is (Create);

---- private, moved here, will work.
   =20
    Type Subject is tagged null record
      with Input =3D> Input;

    function Create return Subject is (null record);
end example;

yields the following error message:
     private function with tagged result must override visible-part functio=
n
     move subprogram to the visible part (RM 3.9.3(10))

Yet, the given paragraph says:
   For an abstract type declared in a visible part, an abstract primitive s=
ubprogram shall not be declared in the private part, unless it is overridin=
g an abstract subprogram implicitly declared in the visible part. For a tag=
ged type declared in a visible part, a primitive function with a controllin=
g result or a controlling access result shall not be declared in the privat=
e part, unless it is overriding a function implicitly declared in the visib=
le part.

Is the error correct? 'Input, 'Output, 'Read & 'Write are implicitly create=
d due to the stream operations/attributes, though arguably they are not fun=
ctions/subprograms.

I should think that it would be perfectly appropriate to place the declarat=
ions of the functions you're assigning to 'Read/'Write/'Input/'Output into =
the private portion of the package.