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Diffstat (limited to 'pod/perltrap.pod')
| -rw-r--r-- | pod/perltrap.pod | 27 |
1 files changed, 26 insertions, 1 deletions
diff --git a/pod/perltrap.pod b/pod/perltrap.pod index 4159777146..8a3e3bcdab 100644 --- a/pod/perltrap.pod +++ b/pod/perltrap.pod @@ -921,6 +921,10 @@ Probably a bug. Perl4-to-Perl5 traps involving precedence order. +Perl 4 has almost the same precedence rules as Perl 5 for the operators +that they both have. Perl 4 however, seems to have had some +inconsistencies that made the behavior differ from what was documented. + =over 5 =item * Precedence @@ -996,13 +1000,34 @@ treats C<$::> as main C<package> =item * Precedence -concatenation precedence over filetest operator? +perl4 had buggy precedence for the file test operators vis-a-vis +the assignment operators. Thus, although the precedence table +for perl4 leads one to believe C<-e $foo .= "q"> should parse as +C<((-e $foo) .= "q")>, it actually parses as C<(-e ($foo .= "q"))>. +In perl5, the precedence is as documented. -e $foo .= "q" # perl4 prints: no output # perl5 prints: Can't modify -e in concatenation +=item * Precedence + +In perl4, keys(), each() and values() were special high-precedence operators +that operated on a single hash, but in perl5, they are regular named unary +operators. As documented, named unary operators have lower precedence +than the arithmetic and concatenation operators C<+ - .>, but the perl4 +variants of these operators actually bind tighter than C<+ - .>. +Thus, for: + + %foo = 1..10; + print keys %foo - 1 + + # perl4 prints: 4 + # perl5 prints: Type of arg 1 to keys must be hash (not subtraction) + +The perl4 behavior was probably more useful, if less consistent. + =back =head2 General Regular Expression Traps using s///, etc. |