Re: Why Perl boolean expression sometimes treated as lvalue?

Well, seems this example makes more sense.

my $a = 0;
my $b = 2;
my $z = \($a && $b);
$$z = 4;
print $a;
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(prints 4)

Comment on Re: Why Perl boolean expression sometimes treated as lvalue? Download Code

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Re^2: Why Perl boolean expression sometimes treated as lvalue? by Anonymous Monk on Feb 08, 2013 at 13:22 UTC
Interesting ... note the parens, perl parses it correctly `$ perl -MO=Deparse,-p -le " $a= 1 && 2; print $a; " BEGIN { $/ = "\n"; $\ = "\n"; } ($a = 2); print($a); -e syntax OK $ perl -MO=Deparse,-p -e " $a && $b = 3; " Can't modify logical and (&&) in scalar assignment at -e line 1, near +"3;" -e had compilation errors. (($a && $b) = 3);` [download] But there is no code to execute this :) its default Can't modify %s http://perl5.git.perl.org/perl.git/blob?f=op.c#l2020 2012 /* FALL THROUGH / 2013 default: 2014 nomod: 2015 if (flags & OP_LVALUE_NO_CROAK) return NULL; 2016 / grep, foreach, subcalls, refgen */ 2017 if (type == OP_GREPSTART \|\| type == OP_ENTERSUB 2018 \|\| type == OP_REFGEN \|\| type == OP_LEAVESUBLV) 2019 break; 2020 yyerror(Perl_form(aTHX_ "Can't modify %s in %s", 2021 (o->op_type == OP_NULL && (o->op_flags & OPf +_SPECIAL) 2022 ? "do block" 2023 : (o->op_type == OP_ENTERSUB 2024 ? "non-lvalue subroutine call" 2025 : OP_DESC(o))), 2026 type ? PL_op_desc[type] : "local")); [download]	[reply] [d/l] [select]

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Re^2: Why Perl boolean expression sometimes treated as lvalue?
by Anonymous Monk on Feb 08, 2013 at 13:22 UTC

Interesting ... note the parens, perl parses it correctly

$ perl -MO=Deparse,-p -le " $a= 1 && 2; print $a; "
BEGIN { $/ = "\n"; $\ = "\n"; }
($a = 2);
print($a);
-e syntax OK

$ perl -MO=Deparse,-p -e "  $a && $b = 3; "
Can't modify logical and (&&) in scalar assignment at -e line 1, near 
+"3;"
-e had compilation errors.
(($a && $b) = 3);
[download]

But there is no code to execute this :) its default Can't modify %s http://perl5.git.perl.org/perl.git/blob?f=op.c#l2020


2012         /* FALL THROUGH */
2013     default:
2014       nomod:
2015         if (flags & OP_LVALUE_NO_CROAK) return NULL;
2016         /* grep, foreach, subcalls, refgen */
2017         if (type == OP_GREPSTART || type == OP_ENTERSUB
2018          || type == OP_REFGEN    || type == OP_LEAVESUBLV)
2019             break;
2020         yyerror(Perl_form(aTHX_ "Can't modify %s in %s",
2021                      (o->op_type == OP_NULL && (o->op_flags & OPf
+_SPECIAL)
2022                       ? "do block"
2023                       : (o->op_type == OP_ENTERSUB
2024                         ? "non-lvalue subroutine call"
2025                         : OP_DESC(o))),
2026                      type ? PL_op_desc[type] : "local"));
[download]

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