On Thursday, 1 October 2020 at 17:29:56 UTC, Mathias LANG wrote:
On Thursday, 1 October 2020 at 16:47:37 UTC, Meta wrote:
This seems ridiculous to me. We now have ANOTHER way of asking
the compiler to choose for us whether to pass by ref or by
value, completely mutually exclusive of auto ref. Where was
the DIP (apologies if I just didn't see it)? Did Walter
approve this? How do we explain the difference between in and
auto ref with (as Andrei would say) a straight face?
Yes we have a 3rd way. Because `auto ref` just doesn't cut it
for most usages, and `-preview=rvaluerefparam` never worked.
You can have a look at the full discussion in the PR that
introduced it (dmd#11000).
I try to summarize a few arguments in favor of it here:
https://github.com/dlang/dmd/pull/11000#issuecomment-674498704
As you can see from the discussion, it's not really something
that was quickly merged, but the results of months of work. So
while it might seems "ridiculous" to you, I'd appreciate if you
could take the time to read through the discussion, as well as
taking a look at Herb Sutter's presentation which was linked.
The key takeaway from that presentation is that instead of
having the users specify *how* to pass the parameter, they
should specify what is the parameter's semantic. In our case,
input (in), output (out), or input/output (ref).
I'm not aware of a situation where you want to use `auto ref`
on a parameter without `const` (or `const` semantic), because
if you intend to modify the parameter, you need to be sure
whether it's `ref` or not. I'm aware some people use it for
forwarding but this has its own set of problem.
I've read the discussion but skipped the presentation. All I see
is Atila expressing distaste for the compiler choosing how to
pass values, and no explicit sign-off from either Walter or Atila
before it was merged.
My objection is not to `in`'s new behaviour (although having
something that functions similarly to auto ref but in subtly
different ways is not good language design, IMO). My objection is
that we have a major change to a language feature, that was
merged without the apparent blessing of either of the two people
who are supposed to be the gatekeepers for these decisions, and
without a DIP (yes, it is behind -preview, but that implies that
this will eventually make it into the language proper). That is
what I am calling "ridiculous". If W or A did approve it and I
just wasn't aware, then I apologize and retract my objection.
