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From: "Robert I. Eachus" <rieachus@attbi.com>
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Newsgroups: comp.lang.ada
Subject: Re: Is the Writing on the Wall for Ada?
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I said:


> But if you want to inherit from two classes  with state, and adjust 
> the state of each based on changes to the other, the na�ve implementation
> isn't possible in Ada, and causes indefinite recursion in C++.
 >
 > What indefinite recursion?

This na�ve implementation:

struct A { int a; virtual void set_a(int aa) { a = aa; } };
struct B { int b; virtual void set_b(int bb) { b = bb; } };

struct AB : A, B {
      void set_a(int aa) { set_a(aa); set_b(aa + 1); }
      void set_b(int bb) { set_a(bb - 1); set_b(bb); }
  };

In Ada, as in C++ you can break the recursion by specificly calling the
operations for the parent classes.  Actually you only need to call the 
super operation for one to break the recursion, but you know what I 
mean.  The point about Ada was that if you write equivalent code, you 
will get wacked at compile time for the set_b call.  (If you "fix" it by 
declaring the subroutine and then providing a separate body, you will 
get it to compile, but you won't get the results you want.)

-- 
                                                        Robert I. Eachus

Ryan gunned down the last of his third white wine and told himself it 
would all be over in a few minutes.  One thing he'd learned from 
Operation Beatrix: This field work wasn't for him. --from Red Rabbit by 
Tom Clancy.