Drew Taylor wrote:
>
> Does anyone have good evidence either way?
I don't see how C<sub { my $foo ; ...> could ever fail to undef $foo, modulo
bugs in perl. A hell of a lot of code wouldn't work, then.
My practice is to never init lexicals to undef/(), and only to '' or 0 if
they might be used before being set to a defined value. Can't see any
reason to = () in perl, where it's set to undef. C's a different question,
where you often get randomish values instead of perl's nice clean undef.
Side note: stay away from the dreaded C<my $f = blah if blurgh> idiom
unless you really understand it and really need it.
Below are some useless benchmarks. The first focuses on the performance of
C<my $foo=()>, the second is an attempt to put it in perspective. Both
on perl 5.6.0. It's a lot slower to initialize (66%). My take is that
it's a minor hit compared to the other things you're usually doing, unless
you do it in a tight inner loop.
- Barrie
Rate my $foo = 7 my $foo = () my $foo = undef my $foo
my $foo = 7 1724138/s -- -14% -14% -71%
my $foo = () 2000000/s 16% -- 0% -66%
my $foo = undef 2000000/s 16% 0% -- -66%
my $foo 5882353/s 241% 194% 194% --
##########################
#!/usr/local/bin/perl -w
use Benchmark qw( cmpthese timethese ) ;
cmpthese(
timethese(
1000000,
{
'my $foo = 7' => sub { my $foo = 7 },
'my $foo = undef' => sub { my $foo = undef },
'my $foo = ()' => sub { my $foo = () },
'my $foo' => sub { my $foo },
},
'none'
)
) ;
open ME, $0 ; print "\n##########################\n", <ME> ;
-----------------------------------------------------------------------
Rate my $foo = undef my $foo = () my $foo = 7 my $foo
my $foo = undef 934579/s -- -2% -7% -36%
my $foo = () 952381/s 2% -- -6% -34%
my $foo = 7 1010101/s 8% 6% -- -30%
my $foo 1449275/s 55% 52% 43% --
##########################
#!/usr/local/bin/perl -w
use Benchmark qw( cmpthese timethese ) ;
my $bar ;
cmpthese(
timethese(
1000000,
{
'my $foo = 7' => sub { my $foo = 7 ; $bar = 12 },
'my $foo = undef' => sub { my $foo = undef ; $bar = 12 },
'my $foo = ()' => sub { my $foo = () ; $bar = 12 },
'my $foo' => sub { my $foo ; $bar = 12 },
},
'none'
)
) ;
open ME, $0 ; print "\n##########################\n", <ME> ;
