Re: Does Perl do constant anonymous hash creation optimisation?

[Thilosophy]

The following (flawed, see below) experiment (prints out the memory location of the static hash) seems to suggest that Perl indeed creates the hash only once:

#!/usr/bin/perl
sub static_hash {

    print { one => 1, two => 2 };
    print $/;
}

static_hash;
static_hash;
static_hash;

planz$ perl /tmp/static.pl 
HASH(0x1801380)
HASH(0x1801380)
HASH(0x1801380)

Update: Okay, forget about that, this just shows that a hash gets created in the same memory location. It could still be a new hash every time. In fact, changing the experiment to use a fresh hash yields exactly the same output:

#!/usr/bin/perl
sub static_hash {

    print { one => $_[0], two => time };
    print $/;
}

static_hash(8);
static_hash(9);
static_hash(10);

[Anonymous Monk]

It definitely does -not- get optimized.

perl -e 'my %bz = (x => 2, y=> 3, z=>4); sub baz { my $x = \%bz }; sub foo { my $x = { x => 1, y => 2, z=>3 } } sub bar { my $x = {x=>shift, y=>shift, z=>shift} } use Benchmark; timethese(-1,{foo=>\&foo,bar=>\&bar,baz=>\&baz});'
Benchmark: running bar, baz, foo for at least 1 CPU seconds...
       bar:  2 wallclock secs ( 1.03 usr +  0.00 sys =  1.03 CPU) @ 607349.51/s (n=625570)
       baz:  1 wallclock secs ( 1.07 usr + -0.01 sys =  1.06 CPU) @ 3462279.25/s (n=3670016)
       foo:  2 wallclock secs ( 1.06 usr +  0.00 sys =  1.06 CPU) @ 618264.15/s (n=655360)

Note the decimal point.