Re: Are there any "bad" Ada constructs?

[Peter Amey <pna@erlang.praxis.co.uk>]

> 
> My question is: Are there any constructs in Ada that are permitted to do
>     two or more different things and still be correct, in a manner that
>     is similar to that listed above?
> 

There are, mostly associated with aliasing, evaluation order and 
elaboration order.  A simple example is:

procedure Init2(X, Y : out integer)
is
begin
  X := 1;
  Y := 2;
end Init2;

The call Init2(A, A); can set A to 1 or 2 because the order of parameter 
association is undefined (I have two validated compilers which actually 
demonstrate this effect).

Ada has a bit of a cop out in that it labels programs whose meaning 
varies in this way "erroneous"; however, applying such a label doesn't 
make the problems any easier to detect or prevent.  Some secure Ada 
subsets such as SPARK are completely free of this form of anomalous 
behaviour.

Peter