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Diffstat (limited to 'pod/perlsub.pod')
| -rw-r--r-- | pod/perlsub.pod | 41 |
1 files changed, 40 insertions, 1 deletions
diff --git a/pod/perlsub.pod b/pod/perlsub.pod index 16babd2092..7212bb5907 100644 --- a/pod/perlsub.pod +++ b/pod/perlsub.pod @@ -159,7 +159,7 @@ Do not, however, be tempted to do this: Because like its flat incoming parameter list, the return list is also flat. So all you have managed to do here is stored everything in @a and -made @b an empty list. See L</"Pass by Reference"> for alternatives. +made @b an empty list. See L<Pass by Reference> for alternatives. A subroutine may be called using the "&" prefix. The "&" is optional in modern Perls, and so are the parentheses if the subroutine has been @@ -504,6 +504,45 @@ like this: } [..normal %ENV behavior here..] +It's also worth taking a moment to explain what happens when you +localize a member of a composite type (i.e. an array or hash element). +In this case, the element is localized I<by name>. This means that +when the scope of the C<local()> ends, the saved value will be +restored to the hash element whose key was named in the C<local()>, or +the array element whose index was named in the C<local()>. If that +element was deleted while the C<local()> was in effect (e.g. by a +C<delete()> from a hash or a C<shift()> of an array), it will spring +back into existence, possibly extending an array and filling in the +skipped elements with C<undef>. For instance, if you say + + %hash = ( 'This' => 'is', 'a' => 'test' ); + @ary = ( 0..5 ); + { + local($ary[5]) = 6; + local($hash{'a'}) = 'drill'; + while (my $e = pop(@ary)) { + print "$e . . .\n"; + last unless $e > 3; + } + if (@ary) { + $hash{'only a'} = 'test'; + delete $hash{'a'}; + } + } + print join(' ', map { "$_ $hash{$_}" } sort keys %hash),".\n"; + print "The array has ",scalar(@ary)," elements: ", + join(', ', map { defined $_ ? $_ : 'undef' } @ary),"\n"; + +Perl will print + + 6 . . . + 4 . . . + 3 . . . + This is a test only a test. + The array has 6 elements: 0, 1, 2, undef, undef, 5 + +In short, be careful when manipulating the containers for composite types +whose elements have been localized. =head2 Passing Symbol Table Entries (typeglobs) |