From @vporton

This is a bug report for perl from porton@​narod.ru,
generated with the help of perlbug 1.40 running under perl 5.20.2.

#!/usr/bin/perl

use strict;
use warnings;

package A;

sub new {
  return bless {}, $_[0];
}

our $AUTOLOAD;
sub AUTOLOAD {
  my ($self, @​args) = @​_;

  print "AUTOLOAD $AUTOLOAD() called.\n";
}

sub can {
  my $self = shift;
 
  return $self->SUPER​::can(@​_) || sub{ $AUTOLOAD=$_[0]; goto &AUTOLOAD }; # http​://www.perlmonks.org/?node_id=8227
}

package main;

my $obj = A->new;

my $method = $obj->can("xxx");
$obj->$method();

__END__

AUTOLOAD() is called with $AUTOLOAD set to the object, instead of being
called with method name, as it should.

I think, this is an error.

Whether it is error or not, please provide a workaround way to call
a dynamic (with name determined at run time) autoload method.

Flags​:
  category=core
  severity=high

Site configuration information for perl 5.20.2​:

Configured by Debian Project at Fri May 15 11​:27​:53 UTC 2015.

Summary of my perl5 (revision 5 version 20 subversion 2) configuration​:
 
  Platform​:
  osname=linux, osvers=3.16.0-4-amd64, archname=i586-linux-gnu-thread-multi-64int
  uname='linux babin 3.16.0-4-amd64 #1 smp debian 3.16.7-ckt9-3~deb8u1 (2015-04-24) i686 gnulinux '
  config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-z,relro -Dlddlflags=-shared -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=i586-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.20 -Darchlib=/usr/lib/i386-linux-gnu/perl/5.20 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/i386-linux-gnu/perl5/5.20 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.20.2 -Dsitearch=/usr/local/lib/i386-linux-gnu/perl/5.20.2 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.20.2 -des'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  use64bitint=define, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-O2 -g',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include'
  ccversion='', gccversion='4.9.2', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  ivtype='long long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=4, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib/gcc/i586-linux-gnu/4.9/include-fixed /usr/include/i386-linux-gnu /usr/lib /lib/i386-linux-gnu /lib/../lib /usr/lib/i386-linux-gnu /usr/lib/../lib /lib
  libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
  perllibs=-ldl -lm -lpthread -lc -lcrypt
  libc=libc-2.19.so, so=so, useshrplib=true, libperl=libperl.so.5.20
  gnulibc_version='2.19'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib -fstack-protector'

Locally applied patches​:
  DEBPKG​:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN.
  DEBPKG​:debian/db_file_ver - http​://bugs.debian.org/340047 Remove overly restrictive DB_File version check.
  DEBPKG​:debian/doc_info - Replace generic man(1) instructions with Debian-specific information.
  DEBPKG​:debian/enc2xs_inc - http​://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @​INC directories.
  DEBPKG​:debian/errno_ver - http​://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes.
  DEBPKG​:debian/libperl_embed_doc - http​://bugs.debian.org/186778 Note that libperl-dev package is required for embedded linking
  DEBPKG​:fixes/respect_umask - Respect umask during installation
  DEBPKG​:debian/writable_site_dirs - Set umask approproately for site install directories
  DEBPKG​:debian/extutils_set_libperl_path - EU​:MM​: set location of libperl.a under /usr/lib
  DEBPKG​:debian/no_packlist_perllocal - Don't install .packlist or perllocal.pod for perl or vendor
  DEBPKG​:debian/prefix_changes - Fiddle with *PREFIX and variables written to the makefile
  DEBPKG​:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets.
  DEBPKG​:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor.
  DEBPKG​:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy.
  DEBPKG​:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable.
  DEBPKG​:debian/mod_paths - Tweak @​INC ordering for Debian
  DEBPKG​:debian/module_build_man_extensions - http​://bugs.debian.org/479460 Adjust Module​::Build manual page extensions for the Debian Perl policy
  DEBPKG​:debian/prune_libs - http​://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need.
  DEBPKG​:fixes/net_smtp_docs - [rt.cpan.org #36038] http​://bugs.debian.org/100195 Document the Net​::SMTP 'Port' option
  DEBPKG​:debian/perlivp - http​://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local
  DEBPKG​:debian/deprecate-with-apt - http​://bugs.debian.org/747628 Point users to Debian packages of deprecated core modules
  DEBPKG​:debian/squelch-locale-warnings - http​://bugs.debian.org/508764 Squelch locale warnings in Debian package maintainer scripts
  DEBPKG​:debian/skip-upstream-git-tests - Skip tests specific to the upstream Git repository
  DEBPKG​:debian/patchlevel - http​://bugs.debian.org/567489 List packaged patches for 5.20.2-6 in patchlevel.h
  DEBPKG​:debian/skip-kfreebsd-crash - http​://bugs.debian.org/628493 [perl #96272] Skip a crashing test case in t/op/threads.t on GNU/kFreeBSD
  DEBPKG​:fixes/document_makemaker_ccflags - http​://bugs.debian.org/628522 [rt.cpan.org #68613] Document that CCFLAGS should include $Config{ccflags}
  DEBPKG​:debian/find_html2text - http​://bugs.debian.org/640479 Configure CPAN​::Distribution with correct name of html2text
  DEBPKG​:debian/perl5db-x-terminal-emulator.patch - http​://bugs.debian.org/668490 Invoke x-terminal-emulator rather than xterm in perl5db.pl
  DEBPKG​:debian/cpan-missing-site-dirs - http​://bugs.debian.org/688842 Fix CPAN​::FirstTime defaults with nonexisting site dirs if a parent is writable
  DEBPKG​:fixes/memoize_storable_nstore - [rt.cpan.org #77790] http​://bugs.debian.org/587650 Memoize​::Storable​: respect 'nstore' option not respected
  DEBPKG​:debian/regen-skip - Skip a regeneration check in unrelated git repositories
  DEBPKG​:fixes/regcomp-mips-optim - [perl #122817] http​://bugs.debian.org/754054 Downgrade the optimization of regcomp.c on mips and mipsel due to a gcc-4.9 bug
  DEBPKG​:debian/makemaker-pasthru - http​://bugs.debian.org/758471 Pass LD settings through to subdirectories
  DEBPKG​:fixes/perldoc-less-R - [rt.cpan.org #98636] http​://bugs.debian.org/758689 Tell the 'less' pager to allow terminal escape sequences
  DEBPKG​:fixes/pod_man_reproducible_date - http​://bugs.debian.org/759405 Support POD_MAN_DATE in Pod​::Man for the left-hand footer
  DEBPKG​:fixes/io_uncompress_gunzip_inmemory - http​://bugs.debian.org/747363 [rt.cpan.org #95494] Fix gunzip to in-memory file handle
  DEBPKG​:fixes/socket_test_recv_fix - http​://bugs.debian.org/758718 [perl #122657] Compare recv return value to peername in socket test
  DEBPKG​:fixes/hurd_socket_recv_todo - http​://bugs.debian.org/758718 [perl #122657] TODO checking the result of recv() on hurd
  DEBPKG​:fixes/regexp-performance - [0fa70a0] http​://bugs.debian.org/777556 [perl #123743] simpify and speed up /.*.../ handling
  DEBPKG​:fixes/failed_require_diagnostics - http​://bugs.debian.org/781120 [perl #123270] Report inaccesible file on failed require
  DEBPKG​:fixes/array-cloning - http​://bugs.debian.org/779357 [perl #124127] [902d169] fix cloning arrays with unused elements
  DEBPKG​:fixes/perldb-threads - http​://bugs.debian.org/779357 [perl #124127] [41ef2c6] lib/perl5db.pl​: Restore noop lock prototype
  DEBPKG​:debian/locale-robustness - http​://bugs.debian.org/782068 [perl #124310] Make t/run/locale.t survive missing locales masked by LC_ALL
  DEBPKG​:fixes/gcc5-errno - http​://bugs.debian.org/778060 [perl #123784] [816b056] Fix Errno.pm generation for gcc-5.0
  DEBPKG​:fixes/h2ph-hex-constants - http​://bugs.debian.org/778060 [perl #123784] [3bea78d] h2ph​: correct handling of hex constants for the preamble
  DEBPKG​:fixes/h2ph-test-inc - http​://bugs.debian.org/778060 [perl #123784] [3359391] lib/h2ph.t to test generated t/_h2ph_pre.ph instead of the system one
  DEBPKG​:fixes/podman-utc - http​://bugs.debian.org/780259 Make the embedded date from Pod​::Man reproducible
  DEBPKG​:fixes/podman-utc-docs - http​://bugs.debian.org/780259 Documentation and test suite updates for UTC fix
  DEBPKG​:fixes/podman-empty-date - http​://bugs.debian.org/780259 Support an empty POD_MAN_DATE environment variable
  DEBPKG​:fixes/podman-pipe - http​://bugs.debian.org/777405 Better errors for man pages from standard input
  DEBPKG​:debian/pod2man-customized - Update porting/customized.dat for pod2man modifications

@​INC for perl 5.20.2​:
  /home/porton/lib/perl/lib
  /etc/perl
  /usr/local/lib/i386-linux-gnu/perl/5.20.2
  /usr/local/share/perl/5.20.2
  /usr/lib/i386-linux-gnu/perl5/5.20
  /usr/share/perl5
  /usr/lib/i386-linux-gnu/perl/5.20
  /usr/share/perl/5.20
  /usr/local/lib/site_perl
  /usr/local/lib/i386-linux-gnu/perl/5.20.1
  /usr/local/share/perl/5.20.1
  .

Environment for perl 5.20.2​:
  HOME=/home/porton
  LANG=en_US.utf8
  LANGUAGE (unset)
  LC_MEASUREMENT=en_US.UTF-8
  LC_MONETARY=en_US.UTF-8
  LC_NUMERIC=en_US.UTF-8
  LC_PAPER=en_US.UTF-8
  LC_TIME=en_US.UTF-8
  LD_LIBRARY_PATH=/usr/local/lib
  LOGDIR (unset)
  PATH=~/bin​:/usr/local/bin​:/usr/bin​:/bin​:/usr/local/games​:/usr/games​:/sbin​:/usr/sbin​:/usr/local/sbin
  PERL5LIB=/home/porton/lib/perl/lib
  PERL_BADLANG (unset)
  SHELL=/bin/bash

From zefram@fysh.org

via RT wrote​:

sub can {
my $self = shift;
return $self->SUPER​::can(@​_) || sub{ $AUTOLOAD=$_[0]; goto &AUTOLOAD }; # http​://www.perlmonks.org/?node_id=8227
}

The logic of this operation requires that $AUTOLOAD in the inner sub
be set to the (post-shift) $_[0] of the ->can method. The $_[0] is
attempting to do that, but, by the semantics of @​_, actually gets the
$_[0] *of the inner sub*, which is the invocant object. The referenced
perlmonks thread is not the source of this mistake.

No Perl bug here.

-zefram

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

From @cowens

On Fri, Jul 24, 2015 at 9​:07 AM, via RT <perlbug-followup@​perl.org> wrote​:
snip

sub AUTOLOAD {
my ($self, @​args) = @​_;

print "AUTOLOAD $AUTOLOAD() called.\n";
}

sub can {
my $self = shift;

return $self->SUPER​::can(@​_) || sub{ $AUTOLOAD=$_[0]; goto &AUTOLOAD }; # http​://www.perlmonks.org/?node_id=8227
}
snip

The $_[0] in the anonymous subroutine is referring to the first
argument to the anonymous subroutine, not to the second argument to
A​::can. @​_ is shadowed in anonymous subroutines, so you can't see the
parent version. To fix this, you can move the value to a lexical and
close over it in the anonymous subroutine. Also note the correct
handling of class methods and the correct formatting of the $AUTOLOAD
value.

#!/usr/bin/perl

use strict;
use warnings;

package A;

sub new {
return bless {}, $_[0];
}

our $AUTOLOAD;
sub AUTOLOAD {
my ($self, @​args) = @​_;

print "AUTOLOAD $AUTOLOAD() called.\n";
}

sub can {
my $self = shift;
my ($name) = @​_;
my $class = ref $self ? ref $self : $self; #handle class methods too

return $self->SUPER​::can(@​_) || sub{ $AUTOLOAD = "$class​::$name"; goto
&AUTOLOAD };
}

package main;

my $obj = A->new;

my $method = $obj->can("xxx");
$obj->$method();

--
Chas. Owens
http​://github.com/cowens
The most important skill a programmer can have is the ability to read.