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From: "Matthew Heaney" <mheaney@on2.com>
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Subject: Re: Ada Popularity: Comparison of Ada/Charles with C++ STL (and Perl)
Date: Thu, 30 Sep 2004 12:50:18 -0400
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"Kevin Cline" <kevin.cline@gmail.com> wrote in message
news:e749549b.0409291942.5790386d@posting.google.com...
>
> There seems to be some confusion between creating a pointer to a
> particular member of a particular record, and the C++ pointer to
> member type.
>
> In C++:
[snip]

There seems to be some confusion between creating an offset to a record
component, and simply using an Ada function pointer:

In Ada:

declare
   type T is record
      A, B : Integer;
   end record;

   function A (O : T) return Integer is
   begin
     return O.A;
   end;

   function B (O : T) return Integer is
   begin
      return O.B;
   end;

   type Query_Type is access function (O : T) return Integer;

   Query : Query_Type := A'Access;

   O1 : T := (3, 5);
   O2 : T := (4, 6);

begin

   pragma Assert (Query (O1) = 3);
   pragma Assert (Query (O2) = 4);

   Query := B'Access;

   pragma Assert (Query (O1) = 5);
   pragma Assert (Query (O2) = 6);

end;



> The availability of pointers to members makes it possible to concisely
> express the mapping between the a data member and the "A" column of a
> database table.

The availability of pointers to local functions makes it possible to
concisely express the mapping between the A record component and the "A"
column of a database table.