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Subject: Interresting difference in Normal-Returns/Expression-Functions and
 Extended-Returns.
From: Shark8 <onewingedshark@gmail.com>
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Date: 2013-04-22T11:27:09-07:00
List-Id: <comp.lang.ada>

I recently ran into unexpected behavior in the differences between a normal=
 return and an extended return [in GNAT]: namely an extended return used to=
 generate items in an array of tasks will *ALWAYS* execute in a sequential =
manner whereas the array generated with an expression-function or normal re=
turn is executed simultaneously.

Is there some subtle difference in the extended return that I'm unaware of?=
 (Is this a bug?)

--------------------
-- Experiment.adb --
--------------------
Pragma Ada_2012;

With
Ada.Text_IO,
Ada.Numerics.Float_Random
;

Procedure Experiment is

    -----------------------------------------------------
    -- RNG; This sets up random numbers for durations. --
    -----------------------------------------------------
    Package RNG is
	Function Random Return Duration;
    Private
	Use Ada.Numerics.Float_Random;
	G : Generator;
	Function Random Return Duration is
	    ( Duration( Random(G) ) );
    End RNG;
   =20
    Package Body RNG is
    Begin
	Ada.Numerics.Float_Random.Reset( G );
    End RNG;
   =20
    --------------------------------------------------
    -- Resource; Protected object handling Text-IO. --
    --------------------------------------------------
   protected Resource is
      procedure Write( Input : In String );
      procedure New_Line;
   private
   end Resource;
   =20
   protected body Resource is
      procedure Write( Input : In String ) is
      begin
         Ada.Text_IO.Put_Line( Input );
      end Write;

      Procedure New_Line is begin Write(""); end New_Line;
   end Resource;
   =20
    ---------------------------------------------------------
    -- Testing; This is the task-type we are playing with. --
    ---------------------------------------------------------
   Task Type Testing( Text : Not Null Access Constant String ) is
    end Testing;


   Task Body Testing is
      D : Duration :=3D RNG.Random; -- Get a random duration.
    Begin
	delay  D; -- Delay for that duration.
      -- Then print the Text for the task as well as the Delay.
      Resource.Write( Text.ALL & ASCII.HT & Duration'Image(D) );
   End Testing;

   =20
    -- Make; these functions make an access-to-tasks for arrays.
    -- Note: these should all be equivelant.
   Function Make_EF(Input : in String) Return Not Null Access Testing is
    ( New Testing( Text =3D> New String'(Input) ) );

   Function Make_ER(Input : in String) Return Not Null Access Testing is
   begin
      Return Result : Not Null Access Testing:=3D New Testing(New String'(I=
nput));
   End Make_ER;

   Function Make_NR(Input : in String) Return Not Null Access Testing is
   begin
      Return New Testing(New String'(Input));
   End Make_NR;

   =20
Begin

    Resource.Write("TEST_1:"& ASCII.HT &"Expression Function");
    TEST_1:
    declare
	Function Make(Input : in String) Return Not Null Access Testing
	       Renames Make_EF;

	P : Constant Array (Positive Range <>) of
	  Not Null Access Constant Testing:=3D
	    ( Make("Bob"), Make("Steve"), Make("Dave"), Make("Joey") );
    begin
	null;
    end TEST_1;
    Resource.New_Line;
    Resource.Write("TEST_2:"& ASCII.HT &"Normal Return Function");
    TEST_2:
    declare
	Function Make(Input : in String) Return Not Null Access Testing
	       Renames Make_NR;

	P : Constant Array (Positive Range <>) of
	  Not Null Access Constant Testing:=3D
	    ( Make("Bob"), Make("Steve"), Make("Dave"), Make("Joey") );
    begin
	null;
    end TEST_2;
    Resource.New_Line;
    Resource.Write("TEST_3:"& ASCII.HT &"Extended Return Function");
    TEST_3:
    declare
	Function Make(Input : in String) Return Not Null Access Testing
	       Renames Make_ER;

	P : Constant Array (Positive Range <>) of
	  Not Null Access Constant Testing:=3D
	    ( Make("Bob"), Make("Steve"), Make("Dave"), Make("Joey") );
    begin
	null;
    end TEST_3;
    Resource.New_Line;
   =20
   Resource.Write( "Terminating." );
End Experiment;