Re^2: return if 0

[massa]

perl -E 'sub result { return 1 if "0" } say result'

yields

0

and

perl -E 'sub result { return 1 if "0 but true" } say result'

yields

1

thus proving your statement :-D

[ikegami]

Not really, but the following does:

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(undef)'
$VAR1 = undef;

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(0    )'
$VAR1 = 0;

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->("0"  )'
$VAR1 = '0';

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(""   )'
$VAR1 = '';

Update: Switched to DD to show the difference between string zero and numerical zero.

[massa]

Look how interesting:

$ perl -MData::Dumper -e 'print Dumper (do { 1 if $_ }) for undef, 0, 
+"0", ""'
$VAR1 = undef;
$VAR1 = 0;
$VAR1 = '0';
$VAR1 = '';
$ perl -MData::Dumper -e 'print Dumper ($_ and 1) for undef, 0, "0", "
+"'
$VAR1 = undef;
$VAR1 = 0;
$VAR1 = '0';
$VAR1 = '';
$ perl -MO=Concise -e 'sub a { 1 if $_ } print a for undef, 0, "0", ""
+'
k  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
3     <;> nextstate(main 2 -e:1) v:{ ->4
j     <2> leaveloop vK/2 ->k
a        <{> enteriter(next->g last->j redo->b) lK/8 ->h
-           <0> ex-pushmark s ->4
-           <1> ex-list lKM ->9
4              <0> pushmark sM ->5
5              <0> undef s ->6
6              <$> const[IV 0] sM ->7
7              <$> const[PV "0"] sM ->8
8              <$> const[PV ""] sM ->9
9           <#> gv[*_] s ->a
-        <1> null vK/1 ->j
i           <|> and(other->b) vK/1 ->j
h              <0> iter s ->i
-              <@> lineseq vK ->-
f                 <@> print vK ->g
b                    <0> pushmark s ->c
e                    <1> entersub[t2] lKS/TARG,1 ->f
-                       <1> ex-list lK ->e
c                          <0> pushmark s ->d
-                          <1> ex-rv2cv sK/128 ->-
d                             <#> gv[*a] s ->e
g                 <0> unstack v ->h
-e syntax OK
$ perl -MO=Concise -e 'sub a { $_ and 1 } print a for undef, 0, "0", "
+"'
k  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
3     <;> nextstate(main 2 -e:1) v:{ ->4
j     <2> leaveloop vK/2 ->k
a        <{> enteriter(next->g last->j redo->b) lK/8 ->h
-           <0> ex-pushmark s ->4
-           <1> ex-list lKM ->9
4              <0> pushmark sM ->5
5              <0> undef s ->6
6              <$> const[IV 0] sM ->7
7              <$> const[PV "0"] sM ->8
8              <$> const[PV ""] sM ->9
9           <#> gv[*_] s ->a
-        <1> null vK/1 ->j
i           <|> and(other->b) vK/1 ->j
h              <0> iter s ->i
-              <@> lineseq vK ->-
f                 <@> print vK ->g
b                    <0> pushmark s ->c
e                    <1> entersub[t2] lKS/TARG,1 ->f
-                       <1> ex-list lK ->e
c                          <0> pushmark s ->d
-                          <1> ex-rv2cv sK/128 ->-
d                             <#> gv[*a] s ->e
g                 <0> unstack v ->h
-e syntax OK

Conclusion: $_ and 1 and 1 if $_ is exactly the same thing. perl compiles it to the same bytecode.

[ikegami]

Indeed. And

if (c()) { f(); g() }

is the same as

c() and do { f(); g() };

$ diff -u \
>   <( perl -MO=Concise,-exec -e'  if (c()) { f(); g() }    ' 2>&1 ) \
>   <( perl -MO=Concise,-exec -e'  c() and do { f(); g() }  ' 2>&1 )
--- /dev/fd/63  2009-07-07 12:25:27.614985473 -0400
+++ /dev/fd/62  2009-07-07 12:25:27.598984321 -0400
@@ -1,6 +1,6 @@
 -e syntax OK
 1  <0> enter
-2  <;> nextstate(main 3 -e:1) v
+2  <;> nextstate(main 2 -e:1) v
 3  <0> pushmark s
 4  <#> gv[*c] s/EARLYCV
 5  <1> entersub[t2] sKS/TARG,1

[zigdon]

Interesting! The last expression evaluated is the string "0". That's false, so the return doesn't fire, but the "0" is actually returned.

Cool example, thanks!