Re: Experimenting with the OOP features in Ada

[Brian Drummond <brian@shapes.demon.co.uk>]

On Mon, 02 Jan 2017 14:11:40 +0000, Brian Drummond wrote:

> On Mon, 02 Jan 2017 05:21:49 -0800, Laurent wrote:
> 
> I suspect you intended something more like
> 
>    Test_Antibiotic := Base_Types.Antibiotics.Create_Name (Name => "Test
> Antibiotic 3");
>    Test_Antibiotic.Set_Code_SIL (Code_SIL => "gen");

More specifically, especially if you're used to some other OO languages, 
is that Ada (2005 and 2012) handle the object.method notation a little 
differently than you may be used to.

You've written a function

   function Create_Code_SIL (Code_SIL : String) return Object;

which takes ONE argument "Code_Sil" and creates a new object containing 
it, and three empty elements...

You were probably expecting a silent "this" argument ... sorry, Ada 
doesn't do that, you explicitly pass the receiver (or "self" or "this") 
to the method (as the Linn Lingo language did).

So a function to set Code_SIL on an existing object would look more like

function Create_Code_SIL (This : Base_Types.Antibiotics.Objects;
                          Code_SIL : String) return Object;

and its implementation

function Create_Code_SIL (This : Base_Types.Antibiotics.Objects;
                          Code_SIL : String) return Object
   is
   begin
      This.Code_SIL := My_Strings.Handle.Create (Value => Code_SIL);
      return This;
   end Create_Code_SIL;

or a Procedure version (the Set_* procedure in my previous post) with an 
In Out parameter called This.

Procedure Set_Code_SIL (This : in out Base_Types.Antibiotics.Objects;
                        Code_SIL => "gen");

Now your function can be called either in traditional Ada-95 syntax with 
both arguments in the argument list, or object.method notation with only 
the second argument. This allows Ada-95 programs to be more easily and 
gradually refactored into Ada-2005 or 2012.

So the following are equivalent:

Test_Antibiotic := Base_Types.Antibiotics.Create_Code_SIL (
                             This => Test_Antibiotic,
                             Code_SIL => "Test Antibiotic 3")

Test_Antibiotic := Test_Antibiotic.Create_Code_SIL 
                            (Code_SIL => "Test Antibiotic 3"); 

but the preferred form would be

Test_Antibiotic.Set_Code_SIL (Code_SIL => "gen");

-- Brian