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From: Ted Dennison <dennison@telepath.com>
Subject: Re: Q: Access subprogram with class type parameters
Date: 2000/03/09
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References: <38C6F379.173A92AF@jhuapl.edu>
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Date: 2000-03-09T00:00:00+00:00
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In article <38C6F379.173A92AF@jhuapl.edu>,
  Rush Kester <Rush.Kester@jhuapl.edu> wrote:
> This is my first attempt at using subprogram access types and class
> programming.
>
> Why doesn't Default_Get_Procedure match Get_Procedure in the
following?
>

>    type Get_Procedure is access procedure (
>      File : in text_io.file_type;
>      Value : out values'class);
>
>    procedure Default_Get_Procedure(
>      File : in text_io.file_type;
>      Value : out Bool_Values) is

Because Values'Class and Bool_Values aren't the same type. You can't
define a procedure type that will take a procedure with a parameter of a
different type than is in the declaration, even if that different type
does happen to have been derived from the one specified.

I made this exact mistake about 3 months ago when I was trying to write
the parsing support for OpenToken.


--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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