Re: An alternative to Unchecked Conversion

[Robert Dewar <robert_dewar@my-deja.com>]

In article <385AD199.D1428985@Boeing.com>,
  Rex Reges <Rex.R.Reges@Boeing.com> wrote:
> >      gnat r
You should NEVER use this construction in Ada 83,
since it is erroneous. Whoever tells you in Ada 83
to use this rather than unchecked conversion is
simply not very knowledgable on the language
and should not be payed much attention.

In Ada 95, it is permissible, though implementation
dependent to use address clauses. There is no requirement
that an address clause be static, but there are restrictions
on what expressions are allowed. A compiler is not required
to accept the exact form above, though many, including GNAT
will allow this form.

In GNAT, a specific warning will be given if you do not use
a pragma Import for the overlaying variable and it requires
initialization. Generally the use of a pragma Import is
always appropriate, since what does and does not require
initialization is implementation dependent.


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