SPUG: return value of assignment operator

BenRifkah Bergsten-Buret mail.spammagnet at gmail.com
Wed Apr 30 12:13:15 PDT 2008

On Wed, Apr 30, 2008 at 10:50 AM, Michael R. Wolf <MichaelRWolf at att.net> wrote:
>  Open questions for discussion:
>   * Where do you rely on assignment returning the LHS?
>   * What definition of "excess" prevents you from using it further?

I haven't used this before but the only place I would consider it is
in a context where low source code character count is preferred.  The
only such context I can think of is in one liners.

Everywhere else I lean toward explicit behavior for readability.

According to my setup* relying on the returned lvalue is less efficient:

benb at enkidu:~$ cat performance_tuning/lhs.pl

use strict;
use Benchmark qw(:all);

my ($x, $y) = (0,1);

cmpthese (9000000, {
  increment_lhs   => sub { ($x = $y)++ },
  increment_separately  => sub { $x = $y; $x++ },

benb at enkidu:~$ perl performance_tuning/lhs.pl
                          Rate increment_separately        increment_lhs
increment_separately 5555556/s                   --                 -28%
increment_lhs        7758621/s                  40%                   --

Of course Benchmark was only able to give reliable calculations at 90
million iterations or more.

-- Ben

* perl -V
Summary of my perl5 (revision 5 version 8 subversion 4) configuration:
    osname=linux, osvers=, archname=i386-linux-thread-multi
    uname='linux ernie #1 thu mar 16 13:11:55 est 2006 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN
-Dcccdlflags=-fPIC -Darchname=i386-linux -Dprefix=/usr
-Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8
-Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5
-Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local
-Dsitearch=/usr/local/lib/perl/5.8.4 -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 -Uusesfio -Uusenm
-Duseshrplib -Dlibperl=libperl.so.5.8.4 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
-DDEBIAN -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE
-fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='3.3.5 (Debian 1:3.3.5-13)', 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',
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libperl.so.5.8.4
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

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