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Date: Sat, 30 Apr 2022 01:57:37 -0700 (PDT)
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Subject: Question on in/out parameters
From: reinert <reinkor@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:63786
List-Id: <comp.lang.ada>

Hello,

I expected an "out" parameter in a procedure to be like declaring the param=
eter "from scratch" (with actual initial default value). For my compiler (G=
NAT Community Edition, May 2021) it seems like the out parameters brings in=
 content from the calling procedure. Should it be like this?

Below is a test program to illustrate.

reinert

with Ada.Containers; use Ada.Containers;
with Ada.Containers.Vectors;
with Ada.Text_IO; use Ada.Text_IO;
procedure test2 is

   package Integer_Vectors is new Ada.Containers.Vectors
       (Index_Type   =3D> Natural, Element_Type =3D> Integer);
   use Integer_Vectors;

   V : Vector :=3D 10 & 20;

   procedure rk_in_out(W : in out Vector) is
   begin
     W.Append(30); W.Append(40);
   end rk_in_out;

   procedure rk_out(W :    out Vector) is
   begin
     W.Clear;  -- I expected this statement to be redundant since W is "out=
 parameter" (try to remove it and see if results remain the same.)?
     W.Append(30); W.Append(40);
   end rk_out;

begin

   New_Line;
   Put ("First V  : ");
   for e of V loop
       Put(e'Image & " ");
   end loop;

   rk_in_out(W =3D> V);
   New_Line;
   Put ("Second V : ");
   for e of V loop
       Put(e'Image & " ");
   end loop;

   rk_out(W =3D> V);
   New_Line;
   Put ("Third V :  ");
   for e of V loop
       Put(e'Image & " ");
   end loop;

end test2;