Re^2: the $_ Special Variable

[chromatic]

in reply to Re: the $_ Special Variable
in thread the $_ Special Variable

Some will argue to use it whenever possible because its one less variable to eat up space in a sub's pad.

I've never heard that.

Ideally, never.

That rules out map and grep then.

[bulk88]

use strict;
use Data::Dumper;
use Devel::Peek;
use B::Deparse;
use B::Concise;
use B 'svref_2object';
use Devel::Size qw(size total_size);

sub printdef {
    foreach (@_){
        chomp;
    }
    foreach(@_){
        print;
    }
}
sub BtoReg{
    my @a = ();
    foreach(@_){
        if($_->isa("B::SPECIAL")){
            print "SPECIAL ".$B::specialsv_name[$$_]."\n";
        }
        else{
        print "ptr ".$$_."\n".Dumper($_->object_2svref());
        }
    }
}
print Dumper(%B::SPECIAL::);

print "\n\n PRINTDEF\n\n";
my $cv = svref_2object(\&printdef);
print $cv;
print "padlist fill ".$cv->PADLIST->FILL()."\n";
my @arr = $cv->PADLIST->ARRAY();
my @a2 = $arr[0]->ARRAY();
print "first PAD ARR\n";
print Dumper([BtoReg(@a2)]);
@a2 = $arr[1]->ARRAY();
print "second PAD ARR\n";
print Dumper([BtoReg(@a2)]);


sub printmy {
    for my $line (@_){
        chomp $line;
    }
    for my $line2 (@_){
        print $line2;
    }
}

print "\n\n PRINTMY\n\n";
$cv = svref_2object(\&printmy);
print $cv;
print "padlist fill ".$cv->PADLIST->FILL()."\n";
@arr = $cv->PADLIST->ARRAY();
@a2 = $arr[0]->ARRAY();
print "first PAD ARR\n";
print Dumper([BtoReg(@a2)]);
@a2 = $arr[1]->ARRAY();
print "second PAD ARR\n";
print Dumper([BtoReg(@a2)]);

print "\n\nprintdef ".size(\&printdef )."\n\n";
print "\n\nprintmy ".size(\&printmy )."\n\n";

print "\n\nprintdef\n\n";
my $walker = B::Concise::compile('-src','-exec',\&printdef);
$walker->();

print "\n\nprintmy\n\n";
$walker = B::Concise::compile('-src','-exec',\&printmy);
$walker->();

dan's custom devel size at C:/perl512/lib/XSLoader.pm line 94.
$VAR1 = "ISA";
$VAR2 = *B::SPECIAL::ISA;


 PRINTDEF

B::CV=SCALAR(0x1409f44)padlist fill 1
first PAD ARR
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
$VAR1 = [
          ""
        ];
second PAD ARR
ptr 21166580
$VAR1 = [];
ptr 3767036
$VAR1 = \*::_;
ptr 8557092
$VAR1 = \undef;
ptr 8557044
$VAR1 = \undef;
ptr 3767036
$VAR1 = \*::_;
ptr 21167812
$VAR1 = \undef;
ptr 3767036
$VAR1 = \*::_;
ptr 3767036
$VAR1 = \*::_;
ptr 21167748
$VAR1 = \undef;
ptr 3767036
$VAR1 = \*::_;
ptr 3767036
$VAR1 = \*::_;
$VAR1 = [
          ""
        ];


 PRINTMY

B::CV=SCALAR(0x1484984)padlist fill 1
first PAD ARR
SPECIAL &PL_sv_undef
ptr 21128756
$VAR1 = \"\$line";
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
ptr 21128612
$VAR1 = \"\$line2";
SPECIAL &PL_sv_undef
SPECIAL &PL_sv_undef
$VAR1 = [
          ""
        ];
second PAD ARR
ptr 21128228
$VAR1 = [];
ptr 21128724
$VAR1 = \undef;
ptr 3767036
$VAR1 = \*::_;
ptr 21128708
$VAR1 = \undef;
ptr 21128660
$VAR1 = \undef;
ptr 21128596
$VAR1 = \undef;
ptr 3767036
$VAR1 = \*::_;
ptr 21128548
$VAR1 = \undef;
$VAR1 = [
          ""
        ];


printdef 1620



printmy 1587



printdef

B::Concise::compile(CODE(0x8292c4))
# 10:     foreach (@_){
1  <;> dbstate(main -2 C:\Documents and Settings\Owner\Desktop\pmpad.p
+l:10) v:*,&,$
2  <0> pushmark sM
3  <#> gv[*_] s
4  <1> rv2av[t2] sKRM/3
5  <#> gv[*_] s
6  <{> enteriter(next->a last->d redo->7) lKS/8
b  <0> iter s
c  <|> and(other->7) vK/1
# 11:         chomp;
7      <;> dbstate(main -3 C:\Documents and Settings\Owner\Desktop\pmp
+ad.pl:11) v:*,&,$
8      <#> gvsv[*_] s
9      <1> schomp[t5] vK/1
a      <0> unstack v
           goto b
d  <2> leaveloop vK/2
# 13:     foreach(@_){
e  <;> dbstate(main 0 C:\Documents and Settings\Owner\Desktop\pmpad.pl
+:13) v:*,&,$
f  <0> pushmark sM
g  <#> gv[*_] s
h  <1> rv2av[t8] sKRM/3
i  <#> gv[*_] s
j  <{> enteriter(next->o last->r redo->k) lKS/8
p  <0> iter s
q  <|> and(other->k) K/1
# 14:         print;
k      <;> dbstate(main -1 C:\Documents and Settings\Owner\Desktop\pmp
+ad.pl:14) v:*,&,$
l      <0> pushmark s
m      <#> gvsv[*_] s
n      <@> print vK
o      <0> unstack s
           goto p
r  <2> leaveloop K/2
s  <1> leavesub[1 ref] K/REFC,1


printmy

B::Concise::compile(CODE(0x1426694))
# 44:     for my $line (@_){
t  <;> dbstate(main 14 C:\Documents and Settings\Owner\Desktop\pmpad.p
+l:44) v:*,&,$
u  <0> pushmark sM
v  <#> gv[*_] s
w  <1> rv2av[t3] sKRM/3
x  <{> enteriter(next->11 last->14 redo->y)[$line:12,14] lKS/LVINTRO
12 <0> iter s
13 <|> and(other->y) vK/1
# 45:         chomp $line;
y      <;> dbstate(main 13 C:\Documents and Settings\Owner\Desktop\pmp
+ad.pl:45) v:*,&,$
z      <0> padsv[$line:12,14] lRM
10     <1> schomp[t4] vK/1
11     <0> unstack v
           goto 12
14 <2> leaveloop vK/2
# 47:     for my $line2 (@_){
15 <;> dbstate(main 17 C:\Documents and Settings\Owner\Desktop\pmpad.p
+l:47) v:*,&,$
16 <0> pushmark sM
17 <#> gv[*_] s
18 <1> rv2av[t7] sKRM/3
19 <{> enteriter(next->1e last->1h redo->1a)[$line2:15,17] lKS/LVINTRO
1f <0> iter s
1g <|> and(other->1a) K/1
# 48:         print $line2;
1a     <;> dbstate(main 16 C:\Documents and Settings\Owner\Desktop\pmp
+ad.pl:48) v:*,&,$
1b     <0> pushmark s
1c     <0> padsv[$line2:15,17] l
1d     <@> print vK
1e     <0> unstack s
           goto 1f
1h <2> leaveloop K/2
1i <1> leavesub[1 ref] K/REFC,1

strangely the my version is smaller than the $_ version according to Devel::Size but you can see the pad names are gone.

[chromatic]

Oh, I believe that $_ isn't in the pad. I've just never heard of anyone using $_ to save the overhead of a pad (as if!).