Strange behavior of map inside @{}

# New Ticket Created by  bcarter-p5pegg.flyinganvil.org 
# Please include the string:  [perl #46543]
# in the subject line of all future correspondence about
this issue. 
# <URL: h
ttp://rt.perl.org/rt3/Ticket/Display.html?id=46543 >



This is a bug report for perl from bcarter-p5pegg.flyinganvil.org,
generated with the help of perlbug 1.35 running under perl
v5.8.8.


------------------------------------------------------------
-----
I'm not sure if this is truly a bug with perl, or if I have
just managed
to confuse myself into a corner case of perl's parser.  But
I have
distilled down what I encountered into the following minimal
script:

  sub r { map [$_], 4; }
  sub p { { shift; } }
  print   'r = ', r(),
       ', r = ', { r(); },
      ', p() = ', p( r() ),
  $/;


  print  "{  +map [1, 2, 3, $_], (4); }" #
prints nothing
  print "${ +map [1, 2, 3, $_], (4); }" #
prints '1 2 3 4'


blead31847 is the latest that I tested this against, but
it does not
seem to vary by perl version.


[Please do not change anything below this line]
------------------------------------------------------------
-----
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl v5.8.8:

Configured by bcarter at Wed Oct  4 10:49:41 CDT 2006.

Summary of my perl5 (revision 5 version 8 subversion 8)
configuration:
  Platform:
    osname=linux, osvers=2.4.22, archname=i686-linux
    uname='linux egg.flyinganvil.org 2.4.22 #6 tue sep 2
17:43:01 pdt 2003 i686 unknown unknown gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef
usemultiplicity=undef
    useperlio=define d_sfio=undef uselargefiles=define
usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -pipe
-I/usr/local/include -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-fno-strict-aliasing -pipe
-I/usr/local/include'
    ccversion='', gccversion='3.2.3', 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='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldl -lm -lcrypt -lutil -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.3.2.so, so=so, useshrplib=false,
libperl=libperl.a
    gnulibc_version='2.3.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef,
ccdlflags='-Wl,-E'
    cccdlflags='-fpic', lddlflags='-shared
-L/usr/local/lib'

Locally applied patches:
    

---
INC
for perl v5.8.8:
    /home/bcarter/perl5lib
    /usr/local/lib/perl5/5.8.8/i686-linux
    /usr/local/lib/perl5/5.8.8
    /usr/local/lib/perl5/site_perl/5.8.8/i686-linux
    /usr/local/lib/perl5/site_perl/5.8.8
    /usr/local/lib/perl5/site_perl
    .

---
Environment for perl v5.8.8:
    HOME=/home/bcarter
    LANG=C
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
   
PATH=/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/usr/games:
.
    PERL5LIB=/home/bcarter/perl5lib
    PERL_BADLANG (unset)
    SHELL=/bin/bash

On 10/18/07, bcarter-p5pegg.flyinganvil.org (via
RT)
<perlbug-followupperl.org>
wrote:
>
>   print  "{  +map [1, 2, 3, $_], (4); }" #
prints nothing
>   print "${ +map [1, 2, 3, $_], (4); }" #
prints '1 2 3 4'
>

the first line, map is in scalar context, and returns 1, the
length of the
array.   has not been defined yet, so nothing is printed.

try this:
$ perl -le ' = qw/a s d f/; print  "{  +map
[1, 2, 3, $_], (4); }" '

the second line, map is in lvalue context (a reference is
being taken to the
result)
so the scalar context takes the first of the list, just like
(qw/a s d f/)
would work

witness:
$ perl -le '($one,$two) = +map [$_],qw/A B/; print $$one'
A

$ perl -le '($one,$two) = +map [$_],qw/A B/; print $$two'
B

$ perl -le '($one,$two) = map [$_],qw/A B/; print $$two'
B

the unary plus doesn't appear to do much.



-- 
non-smoker since 11:31 pm october 10, 2007
"To do good in secret, and shun the world's
applause, is the surest testimony of a virtuous
heart and self-approving conscience."
--  John Polidori  ( http://tinyurl.com/ytm8ba )