Aliasing does not work with closures #15750

p5pRT · 2016-12-05T01:16:18Z

Migrated from rt.perl.org#130263 (status was 'open')

Searchable as RT130263$

p5pRT · 2016-12-05T01:16:18Z

From @cpansprout

perlref says:

B<CAVEAT:> Aliasing does not work correctly with closures. If you try to
alias lexical variables from an inner subroutine or C<eval>, the aliasing
will only be visible within that inner sub, and will not affect the outer
subroutine where the variables are declared. This bizarre behavior is
subject to change.

Fixing this may require the behaviour to change incompatibly, so it really should block the end of the feature’s experimental parole.

Flags:
category=core
severity=low

Site configuration information for perl 5.25.5:

Configured by sprout at Sun Sep 4 14:05:06 PDT 2016.

Summary of my perl5 (revision 5 version 25 subversion 5) configuration:
Derived from: 63b4aac7809db0ef4bfda7d78ee6f3ff9a210238
Platform:
osname=darwin
osvers=12.5.0
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config_args='-DDEBUGGING -de -Accflags=-DPERL_BOOL_AS_CHAR -Dusedevel -Aoptimize=-O0'
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Compiler:
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Linker and Libraries:
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Dynamic Linking:
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Locally applied patches:
uncommitted-changes

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lib
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Environment for perl 5.25.5:
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p5pRT · 2016-12-06T00:59:15Z

From @davidnicol

On Sun, Dec 4, 2016 at 7:16 PM, Father Chrysostomos
<perlbug-followup@perl.org> wrote:

perlref says:

B<CAVEAT:> Aliasing does not work correctly with closures. If you try to
alias lexical variables from an inner subroutine or C<eval>, the aliasing
will only be visible within that inner sub, and will not affect the outer
subroutine where the variables are declared. This bizarre behavior is
subject to change.

Fixing this may require the behaviour to change incompatibly, so it really should block the end of the feature’s experimental parole.

Is there no workaround like the local named subroutine workaround
suggested in that page?

$ perl -lE 'use feature 'refaliasing';my $x=33;my $y=44; sub A{ \$y =
\$x; print $y } A; print $y'
Aliasing via reference is experimental at -e line 1.
33
44

What would it break if this was to get fixed? $y is not declared
within A, but it gets its own dictionary of lexical variable names --
if inner scopes used the outer dictionaries, but only when aliasing,
would that be possible? What all would break if Perl's treatment of
inner lexicals was more like Javascript's, and no pad entry -- or some
kind of "passthrough" pad entry -- was made when lexical variable
names get declared?

--
"Teaching radical novelties is our main safeguard against
dictatorships" -- Edsger W. Dijkstra

p5pRT · 2016-12-06T00:59:15Z

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

p5pRT · 2017-12-13T22:34:37Z

From @djerius

Created by @djerius

A reference alias is not visible in a lexical subroutine defined
in the same scope.

Here's some sample code:

use 5.010;

use strict;
use warnings;

use feature 'refaliasing';
use feature 'lexical_subs';
use Data::Dumper;

sub foo {
\my @a = [ 1, 2, 3, 4 ];
say Dumper \@a;

# this works as expected
sub { say Dumper \@a }->();

# this doesn't work as expected
my sub foo2 { say Dumper \@a };
foo2;
}

foo;

And the output:

Aliasing via reference is experimental at tt.pl line 11.
$VAR1 = [
1,
2,
3,
4
];

$VAR1 = [
1,
2,
3,
4
];

$VAR1 = [];

Thanks!
Diab

Perl Info


Flags:
    category=core
    severity=low

Site configuration information for perl 5.26.1:

Configured by dj at Mon Sep 25 11:01:28 EDT 2017.

Summary of my perl5 (revision 5 version 26 subversion 1) configuration:
   
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Locally applied patches:
    Devel::PatchPerl 1.40


@INC for perl 5.26.1:
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    /home/dj/lib/perl5
    /home/dj/research/lib/perl5
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    /home/dj/.plenv/versions/5.26.1-x86_64-linux_debian-9/lib/perl5/5.26.1/x86_64-linux
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Environment for perl 5.26.1:
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p5pRT · 2017-12-13T23:07:50Z

From zefram@fysh.org

Diab Jerius wrote:

A reference alias is not visible in a lexical subroutine defined
in the same scope.

That's true, and this is a duplicate of [perl #130263].

-zefram

p5pRT · 2017-12-13T23:07:50Z

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

p5pRT added the Severity Low label Oct 19, 2019

xenu removed the Severity Low label Dec 29, 2021

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Aliasing does not work with closures #15750

Aliasing does not work with closures #15750

p5pRT commented Dec 5, 2016

p5pRT commented Dec 5, 2016

p5pRT commented Dec 6, 2016

p5pRT commented Dec 6, 2016

p5pRT commented Dec 13, 2017

p5pRT commented Dec 13, 2017

p5pRT commented Dec 13, 2017

Aliasing does not work with closures #15750

Aliasing does not work with closures #15750

Comments

p5pRT commented Dec 5, 2016

p5pRT commented Dec 5, 2016

From @cpansprout

p5pRT commented Dec 6, 2016

From @davidnicol

p5pRT commented Dec 6, 2016

p5pRT commented Dec 13, 2017

From @djerius

Created by @djerius

p5pRT commented Dec 13, 2017

From zefram@fysh.org

p5pRT commented Dec 13, 2017