How to NOT give new default to parameter of generic procedure parameter?...

How to NOT give new default to parameter of generic procedure parameter?...

[Fred Stluka]

Here's one for the language lawyers.  I don't think there is
a way to do this.  Someone please tell me that I'm wrong.

From within a generic body GEN, I want to call a procedure PROC1 
which was was passed in as a generic parameter PROC.  I want to 
make the call without specifying any parameters, allowing all of 
them to default to the default expressions specified in the 
declaration of PROC1.  I also do not want to re-specify the default
expressions in my declaration of PROC as a generic formal parameter 
to GEN, because this would override the defaults of PROC1 which may
someday be changed.

The best I've been able to do so far is to declare constants with
the values of all of the defaults, and use these constant names on
the declaration of PROC1 and on the declaration of PROC.  Then, as 
long as any future modifier of this code changes the values of the 
constants instead of changing the default values of the parameters 
directly, my generic code will still always use the right default 
values.  

Any better ideas?
--Fred

Fred Stluka                              Internet: stluka@software.org
Software Productivity Consortium         UUNET:    ...!uunet!software!stluka
2214 Rock Hill Rd, Herndon VA 22070 USA 

-- 

Fred Stluka                              Internet: stluka@software.org
Software Productivity Consortium         UUNET:    ...!uunet!software!stluka
2214 Rock Hill Rd, Herndon VA 22070 USA 

Re: How to NOT give new default to parameter of generic procedure parameter?...

[David Collard]

In article <1991Feb14.224435.1512@software.org> stluka@software.org (Fred Stluka) writes:
> Here's one for the language lawyers.  I don't think there is
> a way to do this.  Someone please tell me that I'm wrong.
> 
> From within a generic body GEN, I want to call a procedure PROC1 
> which was was passed in as a generic parameter PROC.  I want to 
> make the call without specifying any parameters, allowing all of 
> them to default to the default expressions specified in the 
> declaration of PROC1.  I also do not want to re-specify the default
> expressions in my declaration of PROC as a generic formal parameter 
> to GEN, because this would override the defaults of PROC1 which may
> someday be changed.
> 

Are either of these options better?  the first takes in your constant
as a generic formal and the second takes in a visible function 
as a generic formal (default).  

--  (1)  --
 generic
   default_for_x : integer;
   with procedure proc1(x : integer := default_for_x);
 procedure gen;

 procedure gen is
 begin
   proc1;
 end gen;
 
 with gen;
 with Text_IO; use Text_IO;
 procedure boss is
   def : integer := 1;
   procedure proc(x : integer := 1) is
   begin
     put_line(integer'image(x));
   end proc;
   procedure mygen is new gen(proc1, def);
 begin
   mygen;
 end boss;

\f
--   (2)   --
generic
  with function default_for_x return integer is <>;
  with procedure proc1(x : integer := default_for_x);
procedure gen;

procedure gen is
begin
  proc1;
end gen;

with gen;
with Text_IO; use Text_IO;
procedure boss is
  function default_for_x return integer is begin return 1; end;

  procedure proc(x : integer := 1) is
  begin
    put_line(integer'image(x));
  end proc;
  procedure mygen is new gen(proc1 => proc);
begin
  mygen;
end boss;



-- 
-----------------------------------------------------------------------
D. Thor Collard                      Internet: collard@software.org
Software Productivity Consortium     UUNET:    ...!uunet!software!collard
2214 Rock Hill Rd, Herndon VA 22070