develooper Front page | perl.perl5.porters | Postings from September 2013

[perl #119943] RFE: localized state of $_ should carry across goto ⊂

Thread Previous | Thread Next
From:
Linda Walsh
Date:
September 22, 2013 18:44
Subject:
[perl #119943] RFE: localized state of $_ should carry across goto ⊂
Message ID:
rt-3.6.HEAD-1873-1379875434-1456.119943-75-0@perl.org
# New Ticket Created by  Linda Walsh 
# Please include the string:  [perl #119943]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=119943 >



This is a bug report for perl from perl-diddler@tlinx.org,
generated with the help of perlbug 1.39 running under perl 5.16.2.


-----------------------------------------------------------------
[Please describe your issue here]

Am proposing a language change (enabled with some pragma like
'goto_forwards_local'), that would allow variables localized
in 1 sub, that forward control via 'goto' to another sub, to
have 'local' variables propagated in the same way arguments
on the call stack are.

Rationale: Various perl commands take a combination of operands.
'_' is sometimes used as an assumed operand in some of these.
If one wishes to pass _ as an assumed operand, and not disturb
the global '_' (which may be read-only and unable to be assigned to),
one needs to localize it.  When the current function ends, this
localization "pops off" as the function exits.

However there is a the case of "goto &sub", that allows passing
control to a peer function to "finish the current sub's work".  I
submit that it should, at least optionally (or, except for the possibilty
of unknown/unlikely edge cases, default to) pass any localized
variables to the parallel sub (target of the &goto).

It appears, currently, that sub-localized variables, unlike a sub's
parameter state on the call stack, are not passed laterally to targets
of a &goto.  I'm not sure how this is useful, *if* the target of 
the &goto is a common "suffix" body for multiply named subs. 

A simple, use case for using multiple names with a common body of
'&goto' code would be for the multiple names to be taken as names in
a hash that would be passed to a common accessor sub, used in lieu 
of each accessor sub needing to incorporate validity checks
(range, type, etc) as well as get/set behaviors.  

The change involves when a localized var is restored to its previous
state -- before the 'goto' or after.  Conceptually, in the above
described usage, having the localization state track the stack's state
and popping off when the call-context is popped, makes more sense
than the current behavior.

However, on the possibility, that I'm simply (likely) not thinking of
a case where one would "&goto" another sub, that is complete unrelated
to the current sub and this would not be desired (or expected), I
would think that, at least initially, the behavior would only be 
activated with a pragma.

Is there a reason why localized vars aren't kept across a &goto and 
not popped until an "end-of-sub" is encountered?

Tnx.



[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
---
This perlbug was built using Perl 5.16.2 - Fri Feb 15 01:17:37 UTC 2013
It is being executed now by  Perl 5.16.2 - Fri Feb 15 01:12:05 UTC 2013.

Site configuration information for perl 5.16.2:

Configured by abuild at Fri Feb 15 01:12:05 UTC 2013.

Summary of my perl5 (revision 5 version 16 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=3.4.6-2.10-default, archname=x86_64-linux-thread-multi
    uname='linux build34 3.4.6-2.10-default #1 smp thu jul 26 09:36:26 utc 2012 (641c197) x86_64 x86_64 x86_64 gnulinux '
    config_args='-ds -e -Dprefix=/usr -Dvendorprefix=/usr -Dinstallusrbinperl -Dusethreads -Di_db -Di_dbm -Di_ndbm -Di_gdbm -Dd_dbm_open -Duseshrplib=true -Doptimize=-fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -Wall -pipe -Accflags=-DPERL_USE_SAFE_PUTENV -Dotherlibdirs=/usr/lib/perl5/site_perl'
    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 -DPERL_USE_SAFE_PUTENV -fno-strict-aliasing -pipe -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -Wall -pipe',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DPERL_USE_SAFE_PUTENV -fno-strict-aliasing -pipe -fstack-protector'
    ccversion='', gccversion='4.7.2 20130108 [gcc-4_7-branch revision 195012]', 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/lib64 -fstack-protector'
    libpth=/lib64 /usr/lib64 /usr/local/lib64
    libs=-lm -ldl -lcrypt -lpthread
    perllibs=-lm -ldl -lcrypt -lpthread
    libc=/lib64/libc-2.17.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.17'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.16.2/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib64 -fstack-protector'

Locally applied patches:
    

---
@INC for perl 5.16.2:
    /home/law/bin/lib
    /usr/lib/perl5/site_perl/5.16.2/x86_64-linux-thread-multi
    /usr/lib/perl5/site_perl/5.16.2
    /usr/lib/perl5/vendor_perl/5.16.2/x86_64-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.16.2
    /usr/lib/perl5/5.16.2/x86_64-linux-thread-multi
    /usr/lib/perl5/5.16.2
    /usr/lib/perl5/site_perl/5.16.2/x86_64-linux-thread-multi
    /usr/lib/perl5/site_perl/5.16.2
    /usr/lib/perl5/site_perl
    .

---
Environment for perl 5.16.2:
    HOME=/home/law
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=C
    LC_CTYPE=en_US.UTF-8
    LD_LIBRARY_PATH=/usr/lib64/mpi/gcc/openmpi/lib64
    LOGDIR (unset)
    PATH=/home/law/bin/lib:/sbin:/usr/local/sbin:/usr/lib64/mpi/gcc/openmpi/bin:/home/law/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/X11R6/bin:/usr/games:/opt/kde3/bin:/usr/lib/mit/bin:/usr/lib/mit/sbin:.:/usr/lib/qt3/bin:/opt/dell/srvadmin/bin:/usr/sbin:/etc/local/func_lib:/home/law/lib
    PERL5OPT=-Mutf8 -CSA -I/home/law/bin/lib
    PERL_BADLANG (unset)
    SHELL=/bin/bash


Thread Previous | Thread Next


nntp.perl.org: Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at ask@perl.org | Group listing | About