How is inheritance implemented in Ada and does it have built in GUI?

Question

Does Ada come with built-in GUI, and does it have the same unique approach to inheritance as does Oberon?

Answer 1

No, Ada does not come with a built-in GUI; but then the closest language that I can think of is PostScript. (Technically, the Java-language does not; though its included library does.) That being said there is a GTK binding (which I haven't used at all) and an OpenGL binding (that I've only played with; and to be honest the OpenGL binding is far thinner a binding than I'd like).

Oberon's inheritance model (as I understand) is single-extension inheritance which is the same as Ada; though Ada does incorporate an Interface system similar to Java. I haven't actually used Oberon, so I can't really provide you with a side-by-side examples for the two, but can show you an example of Ada's.

Base:

Type Base is Abstract Tagged Record
   Null;
End Record; -- Base

-- Base Operations
Procedure Op( Object : In Out Base );
Procedure Dispatching_Op( Object : In Out Base'Class );

Extension:

Type Extended is New Base With Record
  Null;
End Record; -- Extended

Overriding Procedure Op( Object : In Out Extended );

With bodies of, say:

  Procedure Op( Object : In Out Base ) is
  begin
     Put( "Hello" );
  end Op;

  Procedure Dispatching_Op( Object : In Out Base'Class ) is
  begin
     Op( Object );
     Put_Line( " World." );
  end Dispatching_Op;

  Procedure Op( Object : In Out Extended ) is
  begin
     Put( "Goodbye" );
  End Op;

Which given an object of type P {P : K.Base'Class:= K.Extended'(Others => <>);} could be called like so:

P.Dispatching_Op;

And would produce the following results in this instance:

Goodbye World.