SPUG: return value of assignment operator

[Michael R. Wolf]

My results are closer than yours, but contrary to your interpretation,
*both* yours and mine run more iterations per second for the one that relies
on the lvalue.  I'm running Perl cygwin on my XP laptop.

                          Rate increment_separately        increment_lhs
increment_separately 4807692/s                   --                  -8%
increment_lhs        5253940/s                   9%                   --

-- 
Michael R. Wolf
    All mammals learn by playing!
        MichaelRWolf at att.net

> -----Original Message-----
> From: benrifkah at gmail.com [mailto:benrifkah at gmail.com] On Behalf Of
> BenRifkah Bergsten-Buret
> Sent: Wednesday, April 30, 2008 12:13 PM
> To: Michael R. Wolf
> Cc: spug-list at pm.org
> Subject: Re: SPUG: return value of assignment operator
> 
> 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
> #!/usr/bin/perl
> 
> 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:
>   Platform:
>     osname=linux, osvers=2.6.15.6, archname=i386-linux-thread-multi
>     uname='linux ernie 2.6.15.6 #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
> -Dsitelib=/usr/local/share/perl/5.8.4
> -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
> usemultiplicity=define
>     useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
>     use64bitint=undef use64bitall=undef uselongdouble=undef
>     usemymalloc=n, bincompat5005=undef
>   Compiler:
>     cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
> -DDEBIAN -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE
> -D_FILE_OFFSET_BITS=64',
>     optimize='-O2',
>     cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN
> -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',
> lseeksize=8
>     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
>     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'