Andi
At 12:01 PM 3/14/2003 +0000, Ford, Mike [LSS] wrote:
> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Sent: 13 March 2003 19:33 > To: Ford, Mike [LSS] > Cc: 'Andrey Hristov'; [EMAIL PROTECTED] > Subject: RE: [PHP-DEV] Possible problem in the parser > > > At 14:58 13.03.2003, Ford, Mike [LSS] wrote: > > >Just to make this completely clear, in left-associative PHP > > > > b = a==1? 4:a==2? 5:6; > > > >is equivalent to > > > > b = (a==1? 4:a==2)? 5:6; > > > NO it is not equal. Either '==' has higher precedence OR '?:' has. > See one of my previous mails where i showed where the error is.
Yes, it is -- believe me, I've researched this extensively. It is NOT about precedence, but associativity. If you want me to be totally completist about this:
Starting from:
b = a==1? 4:a==2? 5:6;
precedence rules make this equivalent to:
b = (a==1)? 4:(a==2)? 5:6;
but this is still ambiguous -- which ?: phrase do you evaluate first? Associativity provides the answer: in PHP, where ?: is left associative (i.e. the left most ?: is evaluated first), the result is equivalent to:
b = ((a==1)? 4:(a==2))? 5:6;
On the other hand, in c, where ?: is right associative, the equivalent is:
b = (a==1)? 4:((a==2)? 5:6);
which, apart from the additional (unnecessary) parentheses around the == comparisons, is exactly what I said before.
QED
Cheers!
Mike
--------------------------------------------------------------------- Mike Ford, Electronic Information Services Adviser, Learning Support Services, Learning & Information Services, JG125, James Graham Building, Leeds Metropolitan University, Beckett Park, LEEDS, LS6 3QS, United Kingdom Email: [EMAIL PROTECTED] Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211
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