Re: Predeclaration

I learned something today. I thought that with my @x; @x would be undefined but with my @x = (); @x would be a defined but empty list. I guess I was wrong. Here is the experiment I ran. I

my @x;
print 'my @x;',"\n"; &checkdef;
@x = ();
print '@x = ();',"\n"; &checkdef;
@x = (1);
print '@x = (1);',"\n"; &checkdef;
@x = ();
print '@x = ();',"\n"; &checkdef;
undef @x;
print 'undef @x;',"\n"; &checkdef;
@x = ();
print '@x = ();',"\n"; &checkdef;
sub checkdef {
    if (defined (@x)) {
        print "\@x is defined\n"
    } 
    else {
        print "\@x is undefined\n"
    }

}
__OUTPUT__
my @x;
@x is undefined
@x = ();
@x is undefined
@x = (1);
@x is defined
@x = ();
@x is defined
undef @x;
@x is undefined
@x = ();
@x is undefined
[download]

Is anyone else surprised by the results?

flounder

Comment on Re: Predeclaration Select or Download Code

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Re: Predeclaration by Abigail-II (Bishop) on Jul 16, 2002 at 14:49 UTC
Is anyone else surprised by the results? People who read the manual pages will not be surprised. From the manual page about `defined`: Use of "defined" on aggregates (hashes and arrays) is deprecated. It used to report whether memory for that aggregate has ever been allocated. This behavior may disappear in future versions of Perl. You should instead use a simple test for size: if (@an_array) { print "has array elements\n" } if (%a_hash) { print "has hash members\n" } Abigail	[reply] [d/l]
Re: Re: Predeclaration by flounder99 (Friar) on Jul 16, 2002 at 17:39 UTC
Damn documentation! Another case of what I think it does vs. what it really does (and is documented) DWIMing has me spoiled. I think perl's ability to read my mind needs improving! Larry needs to take some lessons from Miss Cleo! (Or at least the acress who plays her) -- flounder ps. For those of you outside the USA (or who never turned on a TV after 11pm in the US) Miss Cleo was a (so called) psychic with a bad fake Jamacan accent who pushed a psychic hotline. The actress who played her recently appeared in court and admitted she was not Jamacan during a fraud investigation.	[reply]