Re: Pass by reference

["Randy Brukardt" <randy@rrsoftware.com>]

"Dan McLeran" <dan.r.mcleran@seagate.com> wrote in message
news:19b0e504.0404090444.376ab672@posting.google.com...
> > The compiler is always free to choose either copy or reference for
> > passing parameters.
>
> This statement seems to contradict the RM and what you've said above.
> The way I read the RM, a by-reference type is passed by reference. No
> choice. A by-value type is passed by value. Again, no choice. The RM
> seems to indicate that the only time a compiler is free to choose is
> for the 'unspecified' types.

That's not quite true. The important thing is that the passing has the
semantics of by-reference or by-copy, not necessarily that that is used.

For instance, we've worked on targets where the standard calling convention
did not support copy back. In order to implement 'in out' parameters of
elementary types on those targets, we do the parameter passing by-reference,
and make a copy at the call-site to insure the by-copy semantics. (We also
use a similar trick for passing large [>32 bit] elementary objects.)

                 Randy.