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Re: my within brackets

by LanX (Sage)
on Oct 14, 2021 at 18:07 UTC ( #11137533=note: print w/replies, xml ) Need Help??


in reply to my within brackets

> But, is there some subtle difference my quick test has not uncovered?

It's the same and it's explicitly documented to be so.

See my VARLIST

The rest is standard list assignment.

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

Replies are listed 'Best First'.
Re^2: my within brackets
by AnomalousMonk (Bishop) on Oct 14, 2021 at 23:06 UTC

    And, indeed, B::Deparse shows it to be so:

    Win8 Strawberry 5.8.9.5 (32) Thu 10/14/2021 17:49:15 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings -MO=Deparse,-p my ($u, $v) = split /,/, 'U,V'; print "'$u' '$v' \n"; (my $w, my $x) = split /,/, 'W,X'; print "'$w' '$x' \n"; ^Z use warnings; use strict 'refs'; (my($u, $v) = split(/,/, 'U,V', 3)); print("'${u}' '${v}' \n"); (my($w, $x) = split(/,/, 'W,X', 3)); print("'${w}' '${x}' \n"); - syntax OK Win8 Strawberry 5.8.9.5 (32) Thu 10/14/2021 18:54:22 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings my ($u, $v) = split /,/, 'U,V'; print "'$u' '$v' \n"; (my $w, my $x) = split /,/, 'W,X'; print "'$w' '$x' \n"; ^Z 'U' 'V' 'W' 'X'
    Same results with Perl version 5.30.3.1.


    Give a man a fish:  <%-{-{-{-<

      B::Deparse is occasionally wrong, it has to guess which code was optimized to what it finally sees.

      But the op-tree is more reliable

      D:\tmp\pm>perl -Mstrict -Mwarnings -MO=Concise my ($u, $v) = split /,/, 'U,V'; __END__ 9 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter v ->2 2 <;> nextstate(main 1 -:1) v:*,&,{,x*,x&,x$,$ ->3 8 <2> aassign[t4] vKS ->9 - <1> ex-list lK ->7 3 <0> pushmark s ->4 6 </> split(/","/)[t3] lK/IMPLIM ->7 4 <$> const[PV "U,V"] s ->5 5 <$> const[IV 3] s ->6 - <1> ex-list lKPRM* ->8 7 <0> padrange[$u:1,2; $v:1,2] RM/LVINTRO,range=2 ->8 - <0> padsv[$u:1,2] sRM*/LVINTRO ->- - <0> padsv[$v:1,2] sRM*/LVINTRO ->- - syntax OK D:\tmp\pm>perl -Mstrict -Mwarnings -MO=Concise (my $u, my $v) = split /,/, 'U,V'; __END__ 9 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter v ->2 2 <;> nextstate(main 1 -:1) v:*,&,{,x*,x&,x$,$ ->3 8 <2> aassign[t4] vKS ->9 - <1> ex-list lK ->7 3 <0> pushmark s ->4 6 </> split(/","/)[t3] lK/IMPLIM ->7 4 <$> const[PV "U,V"] s ->5 5 <$> const[IV 3] s ->6 - <1> ex-list lKPRM* ->8 7 <0> padrange[$u:1,2; $v:1,2] RM/LVINTRO,range=2 ->8 - <0> padsv[$u:1,2] sRM*/LVINTRO ->- - <0> padsv[$v:1,2] sRM*/LVINTRO ->- - syntax OK D:\tmp\pm>

      Now, spot the difference! ;-)

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery

        Now, spot the difference! ;-)

        $ diff -u \ <( perl -Mstrict -Mwarnings -MO=Concise -e'my ($u, $v) = split / +,/, "U,V";' 2>&1 ) \ <( perl -Mstrict -Mwarnings -MO=Concise -e'(my $u, my $v) = split / +,/, "U,V";' 2>&1 ) \ && echo same same

        PS, I usually use -MO=Concise,-exec

        1 <0> enter 2 <;> nextstate(main 1 -e:1) v:*,&,{,x*,x&,x$,$ 3 <0> pushmark s 4 <$> const[PV "U,V"] s 5 <$> const[IV 3] s 6 </> split(/","/)[t3] lK/IMPLIM 7 <0> padrange[$u:1,2; $v:1,2] RM/LVINTRO,range=2 8 <2> aassign[t4] vKS 9 <@> leave[1 ref] vKP/REFC -e syntax OK
Re^2: my within brackets
by Bod (Curate) on Oct 14, 2021 at 19:33 UTC
    it's explicitly documented

    I had looked at the docs for my and didn't find it very explicit at all. It says "If more than one variable is listed, the list must be placed in parentheses" but makes no reference to having the my statement inside the parenthesis. Or am I missing something subtle in the documentation?

    This declaration seems unusual and I don't recall seeing it anywhere else which is why it stood out.

      this

      > "If more than one variable is listed, the list must be placed in parentheses"

      means:

      If VARLIST is

      $x,$y,$z

      you must write

      my ($x,$y,$z)

      The alternative

      my $x,$y,$z

      would only declare $x because of precedence, like

      (my $x),$y,$z

      Hence an alternative to what we want is

      my $x,my $y,my $z

      But since we need a list assignment on the LHS, we still need to put it all into parens

      (my $x,my $y,my $z) = split ...

      because this

      my $x,my $y,my $z = split ...

      would only assign to $z because of precedence°, like

      (my $x),(my $y),(my $z = split ...)

      HTH! :)

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery

      Errata

      s/declare/assign to/ choroba++

      UPDATES

      °) Even worse, it would only be a scalar assignment to $z, i.e. the number of possible splits.

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