C<"">; and when used as a reference that isn't being assigned
to, it is treated as an error. If you enable warnings, you'll
be notified of an uninitialized value whenever you treat C<undef>
-as a string or a number. Well, usually. Boolean ("don't-care")
-contexts, such as:
+as a string or a number. Well, usually. Boolean contexts, such as:
my $a;
if ($a) {}
-are exempt from warnings. Operators such as C<++>, C<-->, C<+=>,
+are exempt from warnings (because they care about truth rather than
+definedness). Operators such as C<++>, C<-->, C<+=>,
C<-=>, and C<.=>, that operate on undefined left values such as:
my $a;
} while $x++ <= $z;
}
+B<NOTE:> The behaviour of a C<my> statement modified with a statement
+modifier conditional or loop construct (e.g. C<my $x if ...>) is
+B<undefined>. The value of the C<my> variable may be C<undef>, any
+previously assigned value, or possibly anything else. Don't rely on
+it. Future versions of perl might do something different from the
+version of perl you try it out on. Here be dragons.
+
=head2 Compound statements
In Perl, a sequence of statements that defines a scope is called a block.
looking back your call-stack at run time to find the LABEL. Such
desperate behavior triggers a warning if you use the C<use warnings>
pragma or the B<-w> flag.
-Unlike a C<foreach> statement, a C<while> statement never implicitly
-localises any variables.
If there is a C<continue> BLOCK, it is always executed just before the
conditional is about to be evaluated again, just like the third part of a
implicitly local to the loop and regains its former value upon exiting
the loop. If the variable was previously declared with C<my>, it uses
that variable instead of the global one, but it's still localized to
-the loop.
+the loop. This implicit localisation occurs I<only> in a C<foreach>
+loop.
The C<foreach> keyword is actually a synonym for the C<for> keyword, so
you can use C<foreach> for readability or C<for> for brevity. (Or because
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