Re^2: Warning for checking with undef

Erm, undef without parens returns a perfectly valid value in that context. The problem is that it's being coerced into a numeric value because of the == which triggers the warning.

What you're thinking of is using undef or shift as a hash key ($h{undef}) or to the left of a => (%a = ( undef => 1 )) where there is some bareword magic going on (strict or no). In those cases it is necessary to use parens or a + to disable the magic.

Update: And you can verify it by looking at the different errors produced. Bareword-ness doesn't enter into it.

freebie:~ 746> cat baz
use warnings;
if( 5 == undef ) { 1 }
if( 5 == "undef" ) { 1 }
freebie:~ 747> perl baz
Argument "undef" isn't numeric in numeric eq (==) at baz line 3.
Use of uninitialized value in numeric eq (==) at baz line 2.
[download]

The first one gripes about comparing against undef, the second because you're comparing a non-numeric value numerically.

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Re^3: Warning for checking with undef by anonymized user 468275 (Curate) on Jul 07, 2005 at 15:00 UTC
I am testing on 5.6.1 and will have to look into it again, because my results look different from others. One world, one people	[reply]
Re^4: Warning for checking with undef by Fletch (Bishop) on Jul 07, 2005 at 15:05 UTC
Yes it evaluates to true, because undef is zero numerically regardless of where it came from. It also triggers warnings from each side when the undefined value is coerced into a number, which is exactly what the OP was seeing. `freebie:~ 755> cat quux use warnings; my $foo = undef; if( $foo == undef ) { print "true\n" } freebie:~ 756> perl quux Use of uninitialized value in numeric eq (==) at quux line 3. Use of uninitialized value in numeric eq (==) at quux line 3. + true` [download] Update: Added something that runs inside the conditional to show that it's not being interpreted as a bareword, both sides trigger the undef-used-as-a-number warning, and that the conditional is true without parens. -- We're looking for people in ATL	[reply] [d/l]
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