foreach loop and local-to-file my variable #9785

p5pRT · 2009-07-02T12:41:48Z

Migrated from rt.perl.org#67162 (status was 'open')

Searchable as RT67162$

p5pRT · 2009-07-02T12:41:50Z

From vincent-perl@vinc17.net

Created by vincent@vinc17.org

Note: the following can be seen either as a perl bug or as
a documentation bug (but perl 5.001 had the same behavior
as perl 5.10.0).

Consider the following cases:

$ perl -e 'foreach $i (1,2) { &foo } sub foo { print "!$i\n" }'
!1
!2
$ perl -e 'my $i; foreach $i (1,2) { &foo } sub foo { print "!$i\n" }'
!
!
$ perl -e 'my $i; foreach (1,2) { $i = $_; &foo } sub foo { print "!$i\n" }'
!1
!2

The result of the second test looks incorrect.

The perlsyn(1) man page says under "Foreach Loops":

The "foreach" loop iterates over a normal list value and sets the
variable VAR to be each element of the list in turn. If the variable
is preceded with the keyword "my", then it is lexically scoped, and is
therefore visible only within the loop. Otherwise, the variable is
implicitly local to the loop and regains its former value upon exiting
the loop. If the variable was previously declared with "my", it uses
that variable instead of the global one, but it's still localized to
the loop. This implicit localisation occurs only in a "foreach" loop.

For the second test, we are in the 3rd case:

If the variable was previously declared with "my", it uses that
variable instead of the global one, but it's still localized to
the loop.

The variable is *not* lexically scoped, so that the $i of the
* my $i
* foreach variable
* in sub foo
lexically represent the same variable.

Now concerning its value, the variable is localized, but this is just
like in the first test: the call to foo is done from the loop, and the
value should be the one assigned in the loop (dynamic scoping).

Perl Info


Flags:
    category=core
    severity=low

Site configuration information for perl 5.10.0:

Configured by Debian Project at Fri Jun 12 21:43:19 UTC 2009.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.6.26-1-vserver-amd64, archname=x86_64-linux-gnu-thread-multi
    uname='linux excelsior 2.6.26-1-vserver-amd64 #1 smp sat jan 10 19:46:42 utc 2009 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.0 -Dsitearch=/usr/local/lib/perl/5.10.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.0 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -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 -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.3.3', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /lib64 /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.9.so, so=so, useshrplib=true, libperl=libperl.so.5.10.0
    gnulibc_version='2.9'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

Locally applied patches:
    


@INC for perl 5.10.0:
    /home/vlefevre/lib/site_perl/x86_64-linux-gnu-thread-multi
    /home/vlefevre/lib/site_perl
    /etc/perl
    /usr/local/lib/perl/5.10.0
    /usr/local/share/perl/5.10.0
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.10
    /usr/share/perl/5.10
    /usr/local/lib/site_perl
    .


Environment for perl 5.10.0:
    HOME=/home/vlefevre
    LANG=POSIX
    LANGUAGE (unset)
    LC_CHARMAP=ISO-8859-1
    LC_COLLATE=POSIX
    LC_CTYPE=en_US.ISO8859-1
    LC_TIME=en_DK
    LD_LIBRARY_PATH=/opt/sge/lib/UNSUPPORTED-lx24-GLIBC-2.9-amd64:/lib64:/home/vlefevre/x86_64/lib:/home/vlefevre/lib
    LOGDIR (unset)
    PATH=/home/vlefevre/bin:/home/vlefevre/x86_64/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/opt/bin:/usr/games:.
    PERL5LIB=/home/vlefevre/lib/site_perl
    PERL_BADLANG (unset)
    SHELL=zsh

p5pRT · 2009-07-03T07:09:15Z

From @davidnicol

Inline Patch

diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod
index 2ba30d8..e466ea8 100644
--- a/pod/perlsyn.pod
+++ b/pod/perlsyn.pod
@@ -405,14 +405,12 @@ X<readline> X<< <> >>
 X<for> X<foreach>

 The C<foreach> loop iterates over a normal list value and sets the
-variable VAR to be each element of the list in turn.  If the variable
-is preceded with the keyword C<my>, then it is lexically scoped, and
-is therefore visible only within the loop.  Otherwise, the variable is
-implicitly local to the loop and regains its former value upon exiting
-the loop.  If the variable was previously declared with C<my>, it uses
-that variable instead of the global one, but it's still localized to
-the loop.  This implicit localisation occurs I<only> in a C<foreach>
-loop.
+variable VAR to be each element of the list in turn.  If the variable is
+preceded by or was previously declared with the keyword C<my>, then it
+is lexically scoped, and is visible only within the loop.  Otherwise,
+the variable is implicitly local to the loop and regains its former
+value upon exiting the loop.  This implicit localisation occurs I<only>
+in a C<foreach> loop.
 X<my> X<local>

 The C<foreach> keyword is actually a synonym for the C<for> keyword, so
@@ -424,7 +422,7 @@ X<$_>
 If any element of LIST is an lvalue, you can modify it by modifying
 VAR inside the loop.  Conversely, if any element of LIST is NOT an
 lvalue, any attempt to modify that element will fail.  In other words,
-the C<foreach> loop index variable is an implicit alias for each item
+the C<foreach> loop index variable gets aliased to each item
 in the list that you're looping over.
 X<alias>

p5pRT · 2009-07-03T07:09:16Z

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

p5pRT added Severity Low distro-Linux type-core labels Oct 18, 2019

xenu removed the affects-5.10 label Nov 19, 2021

xenu removed the Severity Low label Dec 29, 2021

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foreach loop and local-to-file my variable #9785

foreach loop and local-to-file my variable #9785

p5pRT commented Jul 2, 2009

p5pRT commented Jul 2, 2009

p5pRT commented Jul 3, 2009

p5pRT commented Jul 3, 2009

foreach loop and local-to-file my variable #9785

foreach loop and local-to-file my variable #9785

Comments

p5pRT commented Jul 2, 2009

p5pRT commented Jul 2, 2009

From vincent-perl@vinc17.net

Created by vincent@vinc17.org

p5pRT commented Jul 3, 2009

From @davidnicol

p5pRT commented Jul 3, 2009