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From: Ken Garlington <GarlingtonKE@lmtas.lmco.com>
Subject: Converting C++ class to Ada
Date: 1996/12/10
Message-ID: <32ADF183.7195@lmtas.lmco.com>#1/1
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organization: Lockheed Martin Tactical Aircraft Systems
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newsgroups: comp.lang.ada,comp.lang.c++
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Date: 1996-12-10T00:00:00+00:00
List-Id: <comp.lang.ada>


In an attempt to better understand both C++ and Ada, I've been
converting some C++ code into Ada. I'm struggling with this particular
class:

  class CTableXY
  {
  public:
    CMotor&   XMotor;
    CMotor&   YMotor;
    CSwitch&  XLimit;
    CSwitch&  YLimit;
    CTableXY( CMotor& xmotor, CMotor& ymotor,
       CSwitch& xlim, CSwitch& ylim ) :
       XMotor(xmotor), YMotor(ymotor),
       XLimit(xlim), YLimit(ylim) {}
    void SetVelocityX( float vel )
    { XMotor.SetSpeed( vel ); }
    void SetVelocityY( float vel )
    { YMotor.SetSpeed( vel ); }
    int GetSwitchX( void ) { return
      XLimit.isOpen(); }
    int GetSwitchY( void ) { return
      YLimit.isOpen(); }
  };

It seems to me that the straightforward Ada translation is something
like:

  with Motor, Switch;
  package Table_XY is

    type Motor_Access_Type is access all Motor.Object_Type'Class;
    type Switch_Access_Type is access all Switch.Object_Type'Class;

    type Object_Type is record
       X_Motor : Motor_Access_Type;
       Y_Motor : Motor_Access_Type;
       X_Limit : Switch_Access_Type;
       Y_Limit : Switch_Access_Type;
    end record;

    procedure Set_Velocity_X ( Object : in out Object_Type;
                               Velocity : in Motor.Velocity_Type );
    -- and so forth

  end Table_XY;

My main issues:

  (1) What do I do about the constructor? As I understand C++,
      I need to force the user to supply values for the components of
      Object_Type when something of that type is declared. How do I do
this?

  (2) If I'm reading it correctly, the C++ interface exposes the details
of
      the table, although it provides procedures to manipulate it.
However,
      I'm thinking of making Object_Type limited private anyway, since
      otherwise it seems silly to have the procedures/functions that are
      declared here. (More of a style issue than anything...)

Any comments?

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