>perl -MO=Concise -e"$a=1"
6  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
5     <2> sassign vKS/2 ->6                 <--
3        <$> const[IV 1] s ->4
-        <1> ex-rv2sv sKRM*/1 ->5
4           <#> gvsv[*a] s ->5
-e syntax OK

>perl -MO=Concise -e"($a)=1"
8  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
7     <2> aassign[t2] vKS ->8               <--
-        <1> ex-list lK ->5
3           <0> pushmark s ->4
4           <$> const[IV 1] s ->5
-        <1> ex-list lK ->7
5           <0> pushmark s ->6
-           <1> ex-rv2sv sKPRM*/1 ->-
6              <#> gvsv[*a] s ->7
-e syntax OK

##</code><code>##

>perl -le"print( scalar( $a=5 ) );"
5

>perl -le"print( scalar( ($a)=5 ) );"
1

##</code><code>##

>perl -MO=Concise -e"@a=4"
9  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
8     <2> aassign[t3] vKS ->9
-        <1> ex-list lK ->5                <---
3           <0> pushmark s ->4
4           <$> const[IV 4] s ->5
-        <1> ex-list lK ->8                <---
5           <0> pushmark s ->6
7           <1> rv2av[t2] lKRM*/1 ->8
6              <#> gv[*a] s ->7
-e syntax OK