Perl, ternary conditional operator

ternary conditional operator

Author	Message
John Hal #1 / 5	ternary conditional operator Why does this print no? I can't figure it out: ___________________________ #!/usr/bin/perl $director = "else"; $director =~ /else/ ? $redirto = "yes" : $redirto = "no"; print $redirto; ____________________________
Wed, 16 Jul 2003 04:57:43 GMT

Uri Guttma #2 / 5	ternary conditional operator JH> Why does this print no? I can't figure it out: JH> ___________________________ JH> #!/usr/bin/perl JH> $director = "else"; JH> $director =~ /else/ ? $redirto = "yes" : $redirto = "no"; your precedence is wrong. ?: binds tighter than = regardless, you should do it this way: $redirto = $director =~ /else/ ? "yes" : "no" ; uri -- SYStems ARCHitecture, Software Engineering, Perl, Internet, UNIX Consulting The Perl Books Page ----------- http://www.sysarch.com/cgi-bin/perl_books The Best Search Engine on the Net ---------- http://www.northernlight.com
Wed, 16 Jul 2003 05:07:25 GMT

John Li #3 / 5	ternary conditional operator "Uri Guttman" wrote Quote: > >>>>> "JH" == John Hall writes: > JH> Why does this print no? I can't figure it out: > JH> $director = "else"; > JH> $director =~ /else/ ? $redirto = "yes" : $redirto = "no"; > your precedence is wrong. ?: binds tighter than = I couldn't figure it out. I [ use O 'Deparse' ] to get this deparsing $director =~ /else/ ? ($redirto = "yes") : $redirto = "no"; It looks good. Just like a normal [ =~ ? ( = ) : ( = ) ] . Could you further explain what's wrong here? Thank you. John Lin
Fri, 18 Jul 2003 09:09:12 GMT

Eric Bohlm #4 / 5	ternary conditional operator Quote: > "Uri Guttman" wrote >> >>>>> "JH" == John Hall writes: >> JH> Why does this print no? I can't figure it out: >> JH> $director = "else"; >> JH> $director =~ /else/ ? $redirto = "yes" : $redirto = "no"; >> your precedence is wrong. ?: binds tighter than = > I couldn't figure it out. I [ use O 'Deparse' ] to get this deparsing > $director =~ /else/ ? ($redirto = "yes") : $redirto = "no"; > It looks good. Just like a normal [ =~ ? ( = ) : ( = ) ] . > Could you further explain what's wrong here? Your "normal" example has two sets of parens. The deparsed output has only one set. What Uri was saying is that the entire ?: operator (which, as you remember, has three operands) binds tighter than =. The $redirto="yes" will be evaluated properly because it's the second operand of the ternary conditional, but the $redirto="no" won't be evaluated as such because the $redirto gets parsed as the third operand of the conditional, and the entire conditional is taken as the left-hand sign of the final =.
Fri, 18 Jul 2003 09:27:09 GMT

The WebDrago #5 / 5	ternary conditional operator \| your precedence is wrong. ?: binds tighter than = \| \| regardless, you should do it this way: \| \| $redirto = $director =~ /else/ ? "yes" : "no" ; \| \| uri heh I'm glad I'm reading today -- I'd completely forgotten this little factoid. :) -- send mail to mactech (at) webdragon (dot) net instead of the above address. this is to prevent spamming. e-mail reply-to's have been altered to prevent scan software from extracting my address for the purpose of spamming me, which I hate with a passion bordering on obsession.
Fri, 18 Jul 2003 10:59:40 GMT

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