Like many languages, Perl provides for user-defined subroutines.
These may be located anywhere in the main program, loaded in from
other files via the C<do>, C<require>, or C<use> keywords, or
-generated on the fly using C<eval> or anonymous subroutines (closures).
+generated on the fly using C<eval> or anonymous subroutines.
You can even call a function indirectly using a variable containing
its name or a CODE reference.
Like the flattened incoming parameter list, the return list is also
flattened on return. So all you have managed to do here is stored
-everything in C<@a> and made C<@b> an empty list. See L<Pass by
-Reference> for alternatives.
+everything in C<@a> and made C<@b> an empty list. See
+L<Pass by Reference> for alternatives.
A subroutine may be called using an explicit C<&> prefix. The
C<&> is optional in modern Perl, as are parentheses if the
this with C<no strict 'vars'>.
A C<my> has both a compile-time and a run-time effect. At compile
-time, the compiler takes notice of it. The principle usefulness
+time, the compiler takes notice of it. The principal usefulness
of this is to quiet C<use strict 'vars'>, but it is also essential
for generation of closures as detailed in L<perlref>. Actual
initialization is delayed until run time, though, so it gets executed
all the subroutines are called in a list context.
-The current implementation does not allow arrays and hashes to be
-returned from lvalue subroutines directly. You may return a
-reference instead. This restriction may be lifted in future.
-
=head2 Passing Symbol Table Entries (typeglobs)
B<WARNING>: The mechanism described in this section was originally
C<local> operator still shines. In fact, in these three places, you
I<must> use C<local> instead of C<my>.
-=over
+=over 4
+
+=item 1.
-=item 1. You need to give a global variable a temporary value, especially $_.
+You need to give a global variable a temporary value, especially $_.
The global variables, like C<@ARGV> or the punctuation variables, must be
C<local>ized with C<local()>. This block reads in F</etc/motd>, and splits
It particular, it's important to C<local>ize $_ in any routine that assigns
to it. Look out for implicit assignments in C<while> conditionals.
-=item 2. You need to create a local file or directory handle or a local function.
+=item 2.
+
+You need to create a local file or directory handle or a local function.
A function that needs a filehandle of its own must use
C<local()> on a complete typeglob. This can be used to create new symbol
See L<perlref/"Function Templates"> for more about manipulating
functions by name in this way.
-=item 3. You want to temporarily change just one element of an array or hash.
+=item 3.
+
+You want to temporarily change just one element of an array or hash.
You can C<local>ize just one element of an aggregate. Usually this
is done on dynamics:
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