Re: Call by reference vs. call by value

[bobduff@world.std.com (Robert A Duff)]

In article <dewar.837995690@schonberg>, Robert Dewar <dewar@cs.nyu.edu> wrote:
>If you want to think more about this issue, worry about packed arrays
>too. Requiring call by reference would mean that ALL packed arrays have
>to be passed using general bit pointers, which would be unacceptably
>inefficient in the normal case where slices are not passed. Same
>thing for records, all records would have to be passed by bit address,
>just in case the record you are passing is a field in a rcord with a
>record rep clause.

Pascal solved this problem in a simple (but rather ugly) way: It's
illegal to pass a component of a packed array or record as a parameter.
The *programmer* must declare a temp variable, and make a copy.  And
Pascal doesn't have slices.

I suspect part of the reason for Ada's rules (which of course predate
the DS annex by a decade) is to avoid the ugliness of the Pascal rule.
Unfortunately, the Ada rule introduces an implementation dependence that
I find uncomfortable.

- Bob