Re: Access and alias

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

In article <J77H4.418$Qy3.109837@news.pacbell.net>,
  tmoran@bix.com wrote:

> As I understand it, if a function has an access type as a
> parameter, and has a "pragma import", then the compiler is
> required to do whatever might be necessary to convert its idea
> of an access value in Ada to the called language's idea of an
> access value.

This is actually quite wrong from a pure language point of
view, there is absolutely no reason why a convention Ada
access type should look anything like a pointer.

What you say above is strictly only true if the type is
declared to have Convention C on the Ada side.

If the compiler DID use a different representation for the
two, I would say your prescription would be quite wrong, there
is absolutely no requirement in the RM for such conversions,
and pragmatically it would be a bad idea to molest parameters
in this way.

In practice compilers usually use the same representation for
convention Ada and convention C access values, at least for
all cases except pointer-to-unconstrained, so the issue of
conversion does not arise, and that is probably where Tom's
misunderstanding comes from (i.e. this pretty serious
misunderstanding does not affect things most of the time).



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