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Re: What is true and false in Perl?

by ambrus (Abbot)
on Apr 07, 2005 at 19:30 UTC ( #445846=note: print w/replies, xml ) Need Help??


in reply to What is true and false in Perl?

undef # evaluates to "" so it's false -- note, you may get a warni +ng "use of uninitialized value if you are using -w

I belive you can not get such a warning, an undefined value is always false without any warning when interpreted as a boolean.

From perlsyn, section Declarations (it's so well hidden):

A variable holds the undefined value ("undef") until it has been assigned a defined value, which is anything other than "undef". When used as a number, "undef" is treated as 0; when used as a string, it is treated as the empty string, ""; and when used as a reference that isn't being of an uninitialized value whenever you treat "undef" as a string or a number. Well, usually. Boolean contexts, such as
my $a; if ($a) {}
are exempt from warnings (because they care about truth rather than definedness).

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[marto]: oddly the last time I was there I saw a zeppelin in flight for the first time
[Corion]: ambrus: I don't know how far the budget estimate has been overrun yet
[Corion]: marto: Heh ;) No, you were likely at Tegel or Schönefeld, the new one ("BER") will be somewhat outside of Berlin ;)
[marto]: Corion Schoenfeld, but my friend has been telling me about this new airport for about 7-8 years now :P
[marto]: I doubt it even exists as a building site :P
[ambrus]: Corion: does building airports "somewhat outside of" a city ever work? cities always grow around the airport quickly, because it's practical to be close to it, and after that, people start to complain that the airplanes land so close to their house and sh
[ambrus]: ould keep down the noise

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