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[perl #95538] perldiag.pod on defined %hash

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Kevin Ryde
July 24, 2011 20:26
[perl #95538] perldiag.pod on defined %hash
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# New Ticket Created by  Kevin Ryde 
# Please include the string:  [perl #95538]
# in the subject line of all future correspondence about this issue. 
# <URL: >

I found the perldiag.pod description of item "defined(%hash) is
deprecated" unclear.

At first I thought it was threatening another incompatible change, but
if I'm not mistaken it's merely that defined %hash has only ever been a
check for non-empty, which may not be what you intended.  If so then
perhaps a wording like the following could make it clearer,

(D deprecated) C<defined()> is not usually useful on hashes, it merely
checks for non-empty, similar to a hash in boolean context (see
L<perldata>).  If a non-empty check is what you want then just use

    if (%hash) {
       # not empty

If you had C<defined(%Foo::Bar::QUUX)> to check whether such a package
variable exists, then it has never actually done that, but instead
creates the hash if necessary (autovivification) then tests for
non-empty.  If you really want to check existence of a package variable
then look at the glob slot with C<defined *Foo::Bar::QUUX{HASH}> (see

[Please do not change anything below this line]
Site configuration information for perl 5.12.4:

Configured by Debian Project at Tue Jun 28 22:20:03 UTC 2011.

Summary of my perl5 (revision 5 version 12 subversion 4) configuration:
  Derived from: 
    osname=linux, osvers=2.6.32-5-686, archname=i486-linux-gnu-thread-multi-64int
    uname='linux callisto 2.6.32-5-686 #1 smp mon jun 13 04:13:06 utc 2011 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.12 -Darchlib=/usr/lib/perl/5.12 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.12.4 -Dsitearch=/usr/local/lib/perl/5.12.4 -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 -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -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 -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.6.1', 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 /lib /usr/lib /usr/lib/i386-linux-gnu /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=, so=so, useshrplib=true,
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

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