"Matthew Heaney" <matthewjheaney@earthlink.net> wrote in message
news:uu173vtv5.fsf@earthlink.net...
> Jacob Sparre Andersen <sparre@crs4.it> writes:
>
> > That was not really what I was worrying about either.  I couldn't even
> > imagine that somebody would design a language that would allow a and b
> > to access each others variables.
>
> But that's more or less what the multiple views idiom let's you do in
> Ada95.  For example given that we want to "inherit" from both of these
> types:
>
>    type A_Type is tagged limited record
>       X : Integer;
>    end record;
>
>    procedure A_Op (A : in out A_Type);
>
>
>    type B_Type is tagged limited record
>       Y : Integer;
>    end record;
>
>    procedure B_Op (B : in out B_Type);
>
>
> We can use our now-familiar idiom to let C_Type "inherit" from both A
> and B:
>
>    type C_Type;
>
>    type A_View (C : access C_Type) is
>      new A_Type with null record;
>
>    procedure A_Op (A : in out A_View); --override
>
>    type B_View (C : access C_Type) is
>      new B_Type with null record;
>
>    procedure B_Op (B : in out B_View); --override
>
>    type C_Type is tagged limited record
>       A : aliased A_View (C_Type'Access);
>       B : aliased B_View (C_Type'Access);
>       Z : Integer;
>    end record;
>
>
>    procedure A_Op (A : in out A_View) is
>       X : Integer renames A.X;
>       Y : Integer renames A.C.B.Y; -- can see B's data
>       Z : Integer renames A.C.Z;
>    begin
>       null;
>    end;
>
>    procedure B_Op (B : in out B_View) is
>       X : Integer renames B.C.A.X; -- can see A's data
>       Y : Integer renames B.Y;
>       Z : Integer renames B.C.Z;
>    begin
>       null;
>    end;
>

I have a question about this idiom.

Taking your example here I'd like to have a classic example of the following
using that idiom:

I have  Bird class that can fly, chirp, eat, hear and build a nest.
I have a Horse class that can eat, run, walk, hear and sleep

How, using your idiom, would I go about creating a Pegasus class ?

From reading your example it seems to me you're create an aggregation of
TypeA and B from type C.  Perhaps the example I state here might make it
clearer on how the idiom works>?

-- 
St�phane Richard
"Ada World" Webmaster
http://www.adaworld.com




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