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From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Re: Interfaces.C questions
Date: Sun, 19 Mar 2017 19:39:02 +0100
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Xref: news.eternal-september.org comp.lang.ada:46425
Date: 2017-03-19T19:39:02+01:00
List-Id: <comp.lang.ada>

A crude, pure interface version for a GSL quadrature function works. Now 
I have unexpected difficulties with a wrapper, which is a generic package:

generic
    type Real is digits <>;
    type Parameters is private;
package GSL is
    type Real_Function is access function (x: Real) return Real;
    ...

The package body contains the following lines, everything on library level:

    type GSL_Function is record
       func:   access			-- this is line 21
	      function (x: C.double; params: Void_Ptr) return C.double;
       params: Void_Ptr;
    end record;
    pragma Convention (C, GSL_Function);

    real_func:	Real_Function;

    ----%<----------------------------------------------------------

    function func (x: C.double; params: Void_Ptr) return C.double is
    begin
       return C.double (real_func (Real(x)));
    end func;
    pragma Convention (C, func);		-- this is line 37

Later, within a procedure body:

       gslf:	aliased GSL_Function;
    begin
       gslf.func:= func'Access;		-- this is line 66
    ...

I get the following compiler messages and understand nothing:

gsl.adb:37:04: pragma "CONVENTION" requires separate spec and must come 
before body
gsl.adb:66:19: subprogram "func" has wrong convention
gsl.adb:66:19: does not match access to subprogram declared at line 21

  - Separate spec? How?
    Before body? All my other CONVENTION pragmas come after the
    subprogram body, without any problem.
  - No match? Where is the difference?

-- 
Frank Hrebabetzky		+49 / 6355 / 989 5070