On Wed, 14 Aug 2002, Luke Palmer wrote:
> Why? We could make arglists exactly equivilent to the way they're done in
> Perl 5, which is a good way.
>
> sub foo($a, $b, *@c) {...}
>
> Would be exactly equivilent to Perl 5's
>
> sub foo { my ($a, $b, @c) = @_; ... }
I've got another idea. How about using a copy-restore technique?
First, assume all arguments are pass-by-reference, whether constant or not.
Second, allow "is ro" as a modifier to force constant semantics -- in this
case, don't make a copy, just use the reference and refuse to modify it.
Third, allow "is rw" as a modifier to enable copy-restore, and to make the
reference modifiable.
Fourth, copy all named parameters into local variables from the passed
reference (except for "is ro" parameters, which should be aliased) -- and
then keep @_ with the actual references, as in Perl 5. (Unlike Perl 5, the
"is ro" parameters would not be modifiable even via @_.)
Finally, for "is rw" parameters, copy the modified local variable back to
the referenced parameter (the original one, even if @_ was shifted!), but
ONLY for a normal subroutine exit.
This would allow pass-by-value semantics by default for convenience, easily
forced read-only parameters, pass-by-reference semantics when desired, but
with a twist -- if the function aborts (throws an exception), no parameters
have been changed, which offers hassle-free transaction-like atomicity.
If a function really wants to modify its parameter, despite throwing an
exception, it could do so via @_ directly. Or, we could also allow another
modifier "is ref" to use simple (modifiable) pass-by-reference semantics,
but default to copy-restore for "is rw"...
This seems like it could be the best of all worlds -- what do people think?
Deven
