Are there any "bad" Ada constructs?

Are there any "bad" Ada constructs?

[Gordon Dodrill]

The C and C++ language have several constructs that are undefined enough
that two conforming compilers are permitted to give different results and
still be correct.  One example is,

   i = 2;
   a[i] = i++;

Executing the second of these two statements, assuming they are properly 
declared first, a compiler is permitted to assign the value of 2 to either
a[2] or a[3] and be correct.  This construct is stated to be undefined by
the ANSI-C standard, and any compiler can actually do anything it pleases.
I saw one reference that stated there are 150 of these sorts of things in
C and C++.

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?

Thanks,

Gordon

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Re: Are there any "bad" Ada constructs?

[Dennison]

Gordon Dodrill wrote:
> 
> The C and C++ language have several constructs that are undefined enough
> that two conforming compilers are permitted to give different results and
> still be correct.  One example is,

> 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?

In Ada 83, anything defined in the LRM to be "erronious" would fall into
this catagory.

-- 
email    - mailto:dennison@iag.net
homepage - http://www.iag.net/~dennison

Re: Are there any "bad" Ada constructs?

[Jerome Desquilbet]

Gordon,

You may find useful information in Ada Quality and Style Guides at

    http://lglwww.epfl.ch/Ada/Resources/References.html#style

Jerome.
______________________________________________________________________
Jerome Desquilbet                             jDesquilbet@Rational.COM
 ' ^

Re: Are there any "bad" Ada constructs?

[Peter Amey]

> 
> 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

Re: Are there any "bad" Ada constructs?

[George Haddad]

No, just misunderstood ones.   :-)
-- 
I found these opinions on my doorstep, would you please give them a good 
home?