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Hash subscript documentation #9360

Closed p5pRT closed 12 years ago

p5pRT commented 16 years ago

Migrated from rt.perl.org#55158 (status was 'rejected')

Searchable as RT55158$

p5pRT commented 16 years ago

From @ig3

This is a bug report for perl from Ian.Goodacre@​xtra.co.nz\, generated with the help of perlbug 1.35 running under perl v5.8.8.

Dear Perl Maintainers\,

Please consider changing perldata.pod to provide a little more information about hash subscripts. I suggest the following\, but please note that I don't know Perl very well and may have made some mistakes.

*** perldata.pod.orig 2008-04-06 15​:56​:40.000000000 +1200 --- perldata.pod 2008-06-01 10​:11​:26.000000000 +1200 *************** *** 685\,690 **** --- 685\,726 ----

  print "Darwin's First Name is "\, $scientists{"Darwin"}\, "\n";

+ Hash keys are always strings. Hash subscripts that are not strings + are converted to strings before being used as keys. + + A hash subscript may be a bareword\, list or other expression. A bareword + is treated as if it were a quoted string. A list is joined with the + subscript separator C\<$;> (see L\). Any other expression is + evaluated in scalar context and its value is converted to a string. + + Note the difference between arrays\, array slices and lists as hash subscripts. + Arrays and array slices are evaluated in scalar context\, returning the number + of elements in the array and the last element of the array slice respectively\, + while lists are joined with the subscript separator. + + For example​: + + # Given the following array + @​array = ('a'\, 'b'\, 'c'); + + # The following are equivalent + $hash{@​array} = 1; + $hash{'3'} = 1; + + # The following are equivalent\, but different from the above + $hash{@​array[0\,1]} = 1; + $hash{'b'} = 1; + + # The following are equivalent but different from all the above + $hash{'a'\, 'b'\, 'c'} = 1; + $hash{()\,@​array} = 1; + $hash{join($;\, 'a'\, 'b'\, 'c')} = 1; + + Note also that if a reference is used as a hash subscript it is converted + to a string representation which cannot be used as a reference and there is + no simple way to convert the string representation back into a reference. + +   =head2 Slices   X\ X\<array\, slice> X\<hash\, slice>

The reference to the subscript separator and the perlvar documentation would have saved me a lot of time and confusion\, and perhaps it would benefit others like me in the future. I added the bit about references because while I was searching for the explanation of what was going on with the lists I kept encountering queries from people who didn't understand what was happening. If there is a FAQ entry on the issue\, and in particular the issue of not being able to use the string representation of a reference as a reference\, adding a pointer to it would be even better.

Kind regards\, Ian Goodacre

Flags​:   category=docs   severity=wishlist

This perlbug was built using Perl v5.8.8 in the Red Hat build system. It is being executed now by Perl v5.8.8 - Mon Nov 12 14​:44​:38 EST 2007.

Site configuration information for perl v5.8.8​:

Configured by Red Hat\, Inc. at Mon Nov 12 14​:44​:38 EST 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration​:   Platform​:   osname=linux\, osvers=2.6.20-1.3002.fc6xen\, archname=i386-linux-thread-multi   uname='linux xenbuilder1.fedora.redhat.com 2.6.20-1.3002.fc6xen #1 smp mon aug 13 14​:21​:21 edt 2007 i686 athlon i386 gnulinux '   config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp\,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root@​localhost -Dcc=gcc -Dcf_by=Red Hat\, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-linux -Dvendorprefix=/usr -Dsiteprefix=/usr -Duseshrplib -Dusethreads -Duseithreads -Duselargefiles -Dd_dosuid -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dinc_version_list=5.8.7 5.8.6 5.8.5 -Dscriptdir=/usr/bin'   hint=recommended\, useposix=true\, d_sigaction=define   usethreads=define use5005threads=undef useithreads=define usemultiplicity=define   useperlio=define d_sfio=undef uselargefiles=define usesocks=undef   use64bitint=undef use64bitall=undef uselongdouble=undef   usemymalloc=n\, bincompat5005=undef   Compiler​:   cc='gcc'\, ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm'\,   optimize='-O2 -g -pipe -Wall -Wp\,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables'\,   cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/include/gdbm'   ccversion=''\, gccversion='4.1.2 20070925 (Red Hat 4.1.2-27)'\, gccosandvers=''   intsize=4\, longsize=4\, ptrsize=4\, doublesize=8\, byteorder=1234   d_longlong=define\, longlongsize=8\, d_longdbl=define\, longdblsize=12   ivtype='long'\, ivsize=4\, nvtype='double'\, nvsize=8\, Off_t='off_t'\, lseeksize=8   alignbytes=4\, prototype=define   Linker and Libraries​:   ld='gcc'\, ldflags =' -L/usr/local/lib'   libpth=/usr/local/lib /lib /usr/lib   libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc   perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc   libc=/lib/libc-2.6.so\, so=so\, useshrplib=true\, libperl=libperl.so   gnulibc_version='2.6'   Dynamic Linking​:   dlsrc=dl_dlopen.xs\, dlext=so\, d_dlsymun=undef\, ccdlflags='-Wl\,-E -Wl\,-rpath\,/usr/lib/perl5/5.8.8/i386-linux-thread-multi/CORE'   cccdlflags='-fPIC'\, lddlflags='-shared -O2 -g -pipe -Wall -Wp\,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -L/usr/local/lib'

Locally applied patches​:  

@​INC for perl v5.8.8​:   /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi   /usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi   /usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi   /usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi   /usr/lib/perl5/site_perl/5.8.8   /usr/lib/perl5/site_perl   /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi   /usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi   /usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi   /usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi   /usr/lib/perl5/vendor_perl/5.8.8   /usr/lib/perl5/vendor_perl   /usr/lib/perl5/5.8.8/i386-linux-thread-multi   /usr/lib/perl5/5.8.8   .

Environment for perl v5.8.8​:   HOME=/home/ian   LANG=en_US.UTF-8   LANGUAGE (unset)   LD_LIBRARY_PATH (unset)   LOGDIR (unset)  
PATH=/usr/kerberos/bin​:/usr/local/bin​:/usr/bin​:/bin​:/usr/X11R6/bin​:/home/ian/bin​:/sbin   PERL_BADLANG (unset)   SHELL=/bin/bash

p5pRT commented 12 years ago

From @jkeenan

On Sun Jun 01 05​:18​:22 2008\, iang wrote​:

This is a bug report for perl from Ian.Goodacre@​xtra.co.nz\, generated with the help of perlbug 1.35 running under perl v5.8.8.

----------------------------------------------------------------- Dear Perl Maintainers\,

Please consider changing perldata.pod to provide a little more information about hash subscripts. I suggest the following\, but please note that I don't know Perl very well and may have made some mistakes.

Since the patch was submitted inline when the ticket was originally filed\, it perhaps did not get the evaluation it deserved. (The ticket was filed over three years ago but still had status "new" as of tonight.)

I am attaching the patch applied to what I believe is the current location in pod/perldata.pod intended by the original poster.

The reference to the subscript separator and the perlvar documentation would have saved me a lot of time and confusion\, and perhaps it would benefit others like me in the future. I added the bit about references because while I was searching for the explanation of what was going on with the lists I kept encountering queries from people who didn't understand what was happening. If there is a FAQ entry on the issue\, and in particular the issue of not being able to use the string representation of a reference as a reference\, adding a pointer to it would be even better.

Kind regards\, Ian Goodacre

Please review the patch for both accuracy and usefulness.

Thank you very much. Jim Keenan

p5pRT commented 12 years ago

From @jkeenan

55158_perldata_hash_subscript.diff

p5pRT commented 12 years ago

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

p5pRT commented 12 years ago

From @cpansprout

On Fri Jan 06 19​:42​:51 2012\, jkeenan wrote​:

On Sun Jun 01 05​:18​:22 2008\, iang wrote​:

This is a bug report for perl from Ian.Goodacre@​xtra.co.nz\, generated with the help of perlbug 1.35 running under perl v5.8.8.

----------------------------------------------------------------- Dear Perl Maintainers\,

Please consider changing perldata.pod to provide a little more information about hash subscripts. I suggest the following\, but please note that I don't know Perl very well and may have made some mistakes.

Since the patch was submitted inline when the ticket was originally filed\, it perhaps did not get the evaluation it deserved. (The ticket was filed over three years ago but still had status "new" as of tonight.)

I am attaching the patch applied to what I believe is the current location in pod/perldata.pod intended by the original poster.

The reference to the subscript separator and the perlvar documentation would have saved me a lot of time and confusion\, and perhaps it would benefit others like me in the future. I added the bit about references because while I was searching for the explanation of what was going on with the lists I kept encountering queries from people who didn't understand what was happening. If there is a FAQ entry on the issue\, and in particular the issue of not being able to use the string representation of a reference as a reference\, adding a pointer to it would be even better.

Kind regards\, Ian Goodacre

Please review the patch for both accuracy and usefulness.

Iā€™ve just taken a quick glance\, and the part about list vs scalar context makes no sense to me. Forcing scalar context on something that isnā€™t a list is a contradiction in terms\, as it has to be in list context to be a list to begin with.

--

Father Chrysostomos

p5pRT commented 12 years ago

From @cpansprout

On Mon Jan 09 13​:38​:17 2012\, sprout wrote​:

On Fri Jan 06 19​:42​:51 2012\, jkeenan wrote​:

On Sun Jun 01 05​:18​:22 2008\, iang wrote​:

This is a bug report for perl from Ian.Goodacre@​xtra.co.nz\, generated with the help of perlbug 1.35 running under perl v5.8.8.

----------------------------------------------------------------- Dear Perl Maintainers\,

Please consider changing perldata.pod to provide a little more information about hash subscripts. I suggest the following\, but please note that I don't know Perl very well and may have made some mistakes.

Since the patch was submitted inline when the ticket was originally filed\, it perhaps did not get the evaluation it deserved. (The ticket was filed over three years ago but still had status "new" as of tonight.)

I am attaching the patch applied to what I believe is the current location in pod/perldata.pod intended by the original poster.

The reference to the subscript separator and the perlvar documentation would have saved me a lot of time and confusion\, and perhaps it would benefit others like me in the future. I added the bit about references because while I was searching for the explanation of what was going on with the lists I kept encountering queries from people who didn't understand what was happening. If there is a FAQ entry on the issue\, and in particular the issue of not being able to use the string representation of a reference as a reference\, adding a pointer to it would be even better.

Kind regards\, Ian Goodacre

Please review the patch for both accuracy and usefulness.

Iā€™ve just taken a quick glance\, and the part about list vs scalar context makes no sense to me. Forcing scalar context on something that isnā€™t a list is a contradiction in terms\, as it has to be in list context to be a list to begin with.

Also\, it is repeating some information in the ā€˜Multi-dimensional array emulationā€™ section that follows shortly thereafter.

In other words\, it seems that part of perldata needs a more careful rewrite/expansion. This patch I think would make the document more incoherent than it already is.

--

Father Chrysostomos

p5pRT commented 12 years ago

From @jkeenan

On Mon Jan 09 13​:42​:06 2012\, sprout wrote​:

On Mon Jan 09 13​:38​:17 2012\, sprout wrote​:

On Fri Jan 06 19​:42​:51 2012\, jkeenan wrote​:

On Sun Jun 01 05​:18​:22 2008\, iang wrote​:

This is a bug report for perl from Ian.Goodacre@​xtra.co.nz\, generated with the help of perlbug 1.35 running under perl v5.8.8.

----------------------------------------------------------------- Dear Perl Maintainers\,

Please consider changing perldata.pod to provide a little more information about hash subscripts. I suggest the following\, but please note that I don't know Perl very well and may have made some mistakes.

Please review the patch for both accuracy and usefulness.

Iā€™ve just taken a quick glance\, and the part about list vs scalar context makes no sense to me. Forcing scalar context on something that isnā€™t a list is a contradiction in terms\, as it has to be in list context to be a list to begin with.

Also\, it is repeating some information in the ā€˜Multi-dimensional array emulationā€™ section that follows shortly thereafter.

In other words\, it seems that part of perldata needs a more careful rewrite/expansion. This patch I think would make the document more incoherent than it already is.

I'm going to mark this as 'rejected'. If we need the "more careful rewrite/expansion" of perldata.pod Father C mentioned\, we should open a new ticket for that.

Thank you very much. Jim Keenan

p5pRT commented 12 years ago

@jkeenan - Status changed from 'open' to 'rejected'