Re^4: return if 0

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
[download]

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

[]s, HTH, Massa (κς,πμ,πλ)

Comment on Re^4: return if 0 Select or Download Code

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Re^5: return if 0 by ikegami (Patriarch) on Jul 07, 2009 at 16:07 UTC
Indeed. And `if (c()) { f(); g() }` [download] is the same as `c() and do { f(); g() };` [download] `$ 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` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^5: return if 0
by ikegami (Patriarch) on Jul 07, 2009 at 16:07 UTC

Indeed. And

if (c()) { f(); g() }
[download]

c() and do { f(); g() };
[download]

$ 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
[download]

[reply]
[d/l]
[select]