permit \escape on right hand side of my

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Migrated from rt.perl.org#127531 (status was 'resolved')

Searchable as RT127531$

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From @rjbs

This is pretty useful​:

  perl -Mexperimental=refaliasing \
  -E 'my $x = [1,2,3]; \my @​y = $x; say for @​y'

...but the question I keep hearing is "why is the backslash on the my and not
the variable?"

The answer is not weird. It's pre-existing syntax to get a reference to a new
variable. It's still confusing, though, because people expect to be able to
write​:

  my \@​y = $x;

I even got this question from Larry.

We should allow that. It would also be good to allow​:

  my ($x, \@​y, \%z) = @​_;

...which means we should then allow​:

  sub foo ($x, \@​y, \%z) { ... }

I would use the *heck* out of that feature.

--
rjbs

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From @cpansprout

On Fri Feb 12 19​:03​:22 2016, rjbs wrote​:

This is pretty useful​:

perl -Mexperimental=refaliasing \
-E 'my $x = [1,2,3]; \my @​y = $x; say for @​y'

...but the question I keep hearing is "why is the backslash on the my
and not
the variable?"

The answer is not weird. It's pre-existing syntax to get a reference
to a new
variable. It's still confusing, though, because people expect to be
able to
write​:

my \@​y = $x;

I even got this question from Larry.

That surprised me. After all, I was just following his existing Perl 5 syntax.

We should allow that. It would also be good to allow​:

my ($x, \@​y, \%z) = @​_;

That begs the question of what

  $x = my \@​y;

would do. I imagine it would be the same as

  $x = \my @​y;

no?

...which means we should then allow​:

sub foo ($x, \@​y, \%z) { ... }

I would use the *heck* out of that feature.

BTW, is anybody using for \@​x (...) yet?

--

Father Chrysostomos

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The RT System itself - Status changed from 'new' to 'open'

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From @rjbs

On Sat Feb 13 09​:48​:36 2016, sprout wrote​:

On Fri Feb 12 19​:03​:22 2016, rjbs wrote​:

I even got this question from Larry.

That surprised me. After all, I was just following his existing Perl
5 syntax.

I think that the feature looks so new that it's easy to forget how it's using existing syntax, especially since it's syntax one is fairly unlikely to use.

That begs the question of what

$x = my \@​y;

would do. I imagine it would be the same as

$x = \my @​y;

That's my thinking as well.

BTW, is anybody using for \@​x (...) yet?

I believe I have used "for my \%x" a few times, if this meets your criteria. :)

--
rjbs

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From @cpansprout

On Sat Feb 13 18​:58​:46 2016, rjbs wrote​:

On Sat Feb 13 09​:48​:36 2016, sprout wrote​:

That begs the question of what

$x = my \@​y;

would do. I imagine it would be the same as

$x = \my @​y;

That's my thinking as well.

Would rvalue use of ‘my \’ be governed by the experimental​::refaliasing feature feature? Would they produce an experimental warning?

--

Father Chrysostomos

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From @ap

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2016-05-18 08​:23]​:

Would rvalue use of ‘my \’ be governed by the
experimental​::refaliasing feature feature? Would they produce an
experimental warning?

The value of the refaliasing feature does not depend on whether the new
ref constructor syntax works out, and the new syntax may fail to work
out due to edge cases that could have nothing to do with refaliasing.

I think they should be separate experiments.

Would refaliasing automatically adopt the new syntax if it is introduced
as a general synonym for the old syntax, or would the features have to
be made to work with each other? If they are highly interdependent, then
maybe the new declare-and-ref syntax experiment ought to wait for the
conclusion of the refaliasing experiment so that each can be evaluated
separately.

Regards,
--
Aristotle Pagaltzis // <http​://plasmasturm.org/>

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From @cpansprout

On Fri May 20 19​:53​:40 2016, aristotle wrote​:

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2016-05-18 08​:23]​:

Would rvalue use of ‘my \’ be governed by the
experimental​::refaliasing feature feature? Would they produce an
experimental warning?

The value of the refaliasing feature does not depend on whether the new
ref constructor syntax works out, and the new syntax may fail to work
out due to edge cases that could have nothing to do with refaliasing.

I think they should be separate experiments.

Would refaliasing automatically adopt the new syntax if it is introduced
as a general synonym for the old syntax, or would the features have to
be made to work with each other?

They would not be interdependent. In fact, the new syntax would just be a matter of switching the two tokens around in the lexer, which is kinda hard to get wrong, so I wonder whether it even needs to be experimental, except as a matter of principle.

Assuming the latter (principle), what would we call it? my_whack? (Though I usually drop the h for that slang term​: my_wack.) my_refcons?

(BTW, not having it experimental would make the implementation a bit easier.)

--

Father Chrysostomos

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From @cpansprout

On Fri May 20 22​:03​:00 2016, sprout wrote​:

In fact, the new syntax would just
be a matter of switching the two tokens around in the lexer

See the sprout/mywack branch. It’s a six-line patch.

--

Father Chrysostomos

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From @cpansprout

On Fri May 20 22​:31​:49 2016, sprout wrote​:

On Fri May 20 22​:03​:00 2016, sprout wrote​:

In fact, the new syntax would just
be a matter of switching the two tokens around in the lexer

See the sprout/mywack branch. It’s a six-line patch.

Oh, but what about my(\$a, $b, \$c)? If that should be permitted, then it is not just a six-line patch, but it will still not interfere with refaliasing. And I still don’t know what to call it if it will be experimental.

--

Father Chrysostomos

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From @rjbs

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2016-05-21T14​:58​:38]

Oh, but what about my(\$a, $b, \$c)? If that should be permitted, then it is
not just a six-line patch, but it will still not interfere with refaliasing.

I'd think so, imagining something like​:

  my ($self, \@​arg) = @​_;

And I still don’t know what to call it if it will be experimental.

I'm not too worried about a name. refs_in_my?

--
rjbs

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From @cpansprout

On Sun May 22 18​:06​:43 2016, perl.p5p@​rjbs.manxome.org wrote​:

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2016-05-
21T14​:58​:38]

Oh, but what about my(\$a, $b, \$c)? If that should be permitted,
then it is
not just a six-line patch, but it will still not interfere with
refaliasing.

I'd think so, imagining something like​:

my ($self, \@​arg) = @​_;

You do realise, I hope, that $_[1] is expected to be an array ref, there?

And I still don’t know what to call it if it will be experimental.

I'm not too worried about a name. refs_in_my?

I’m been thinking of declared_refs, since it applies to the two other *declarators* as well.

--

Father Chrysostomos

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From @cpansprout

If \local $x = $foo works, then local \$x should, do.

But what about delete local \$foo{bar}?

Should I duck?

--

Father Chrysostomos

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From @demerphq

I hate this syntax for exactly this type of ugly edge case. Better to
follow the data​::alias syntax and introduce a new keyword.
On 22 May 2016 22​:38, "Father Chrysostomos via RT" <
perlbug-followup@​perl.org> wrote​:

If \local $x = $foo works, then local \$x should, do.

But what about delete local \$foo{bar}?

Should I duck?

--

Father Chrysostomos

---
via perlbug​: queue​: perl5 status​: open
https://rt-archive.perl.org/perl5/Ticket/Display.html?id=127531

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From @cpansprout

On Sun May 22 19​:51​:58 2016, demerphq wrote​:

I hate this syntax

Are you referring to the use of backslashes?

for exactly this type of ugly edge case.

I was half joking about delete local \$foo{bar}. That can remain a syntax error.

Better to
follow the data​::alias syntax and introduce a new keyword.

Data​::Alias has a smart-match-like list of which types of syntax passed to the function will result in aliasing. I don’t think we should follow that route. With \ notation, the intent is always clear. With Data​::Alias, I find that not to be the case. I have tried learning how to use it, but it just confuses me.

Also, you end up with the whole issue again of whether

  alias @​x = @​y

should alias the arrays or the individual elements. The fact that we have a distinction between \@​a and \(@​a) that people already know about was one of the main reasons for going with that notation.

--

Father Chrysostomos

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From @cpansprout

The sprout/mywack contains what I believe is a working implementation, but it needs docs (including perldiag entries) and tests. I hope someone can take over from here, because I don’t know when I will next have time.

Things to test for​:

my \$a # equivalent to \my $a
my \($a,$b) # equivalent to \my($a, $b)
my (\($a,$b)) # same
my (\$a, $b) # equivalent to (\my $a, $b)
my \$a : foo
my \$a ** 1 # should be equivalent to \my $a ** 1, which is
  # \(my $a ** 1), which is an error
my \\$a # if the declarator can penetrate one backslash, it will also
  # penetrate two; equiv. to \\my $a
my (\\$a)
my (\$a) :attr

foreach my \$x ($y) { ... }

ditto with state/our/local (except that local does not take attributes or work in foreach).

Note that assignment to ‘my \$a : foo’ does not currently work, except with ‘our’ (bug #128183). That is not related to the my\ syntax per se.

--

Father Chrysostomos