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Re: Pre-RFC: Optional Chaining

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July 26, 2022 10:15
Re: Pre-RFC: Optional Chaining
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On Sun, Jul 17, 2022 at 09:23:32PM +0200, Philippe Bruhat (BooK) wrote:
> On Thu, Oct 28, 2021 at 02:39:15PM -0300, breno wrote:
> > 
> > ## Rejected Ideas
> > 
> > I am unaware whether this feature has already been proposed for Perl 5
> > in the past.
> > 
> For completeness, I have (finally) looked in the archives for previous
> proposals for the same feature. It used to be called "safe dereference"
> or "safe arrow", and was discussed over a decade ago.
> ...
> It would be worth reading them, in case some of things discussed then
> were not discussed this time around. And maybe a ten years old patch can
> still be somewhat useful.

After sending this, I felt obligated to read the 180+ emails in the
aforementioned threads.

Here are some highlights from the conversations:
* it started as &&-> and after much discussion and proposed alternatives about what the arrow
  could look like, Jesse Vincent (then pumpking) settled on ?->
* a similar discussion about using a pragma happened, and reached
  a similar conclusion
* the dereferencing overload operations were mentionned, and I _think_
  the consensus was that there's no need to add new overload methods related
* what happens when the ?-> is part of an lvalue (and returns undef)?
* one example of autovivification in perldoc -f exists was mentionned
  I expect it would "just work as expected" with ?->
* David Caldwell sent two sets of patches, I'm sure there's interesting
  bits to look at in them, even if they don't apply anymore
* the ?-> (deref if defined) vs ->? (return undef if not can) came up,
  this makes me thinks that once we have ?-> (topic of this RFC) and
  ->? (if someone writes the RFC for it), then surely we must have ?->?
* the case of the hash key pointing to undef was discussed
  ( $h->{foo}?->method() where the foo key does not exist vs the foo key
    pointing to the value undef would behave the same)
* all the examples and counter examples in those threads would make
  great test cases
* several people complained about the keyboard gymnastics needed to
  type ?-> (but nobody compared that to the thing it replaces)
* being able to use the question mark (`?`) inside operators seem related
  to the ?PAT? deprecation.

Names I've seen used for it:
* safe arrow
* defined dereference
* safe dereference
* maybe dereference
* safe-dereferencing arrow 
* short-circuiting dereference
* conditional dereference
* defreference
* Twister™ (because of the difficult key combination needed to type it)
* undef-safe de-ref
* defined and dereference

My favorite quote from those threads, from Aristotle Pagaltzis, which I
think applies remarkably to today's post-facts trends:

> How can an opinion not founded in fact be changed by any change to
> the factual situation?

 Philippe Bruhat (BooK)

 Friendship is just brotherhood with a choice of brothers.
                                                 (Moral from Groo #9 (Image))

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