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.
}
Notice how this (unprototyped) function doesn't care whether it was
-passed real scalars or arrays. Perl sees all arugments as one big,
+passed real scalars or arrays. Perl sees all arguments as one big,
long, flat parameter list in C<@_>. This is one area where
Perl's simple argument-passing style shines. The C<upcase()>
function would work perfectly well without changing the C<upcase()>
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
an argument to defined() or undef(). Nor is it optional when you
want to do an indirect subroutine call with a subroutine name or
reference using the C<&$subref()> or C<&{$subref}()> constructs,
-although the C<$subref-E<gt>()> notation solves that problem.
+although the C<< $subref->() >> notation solves that problem.
See L<perlref> for more about all that.
Subroutines may be called recursively. If a subroutine is called
function in all capitals is a loosely-held convention meaning it
will be called indirectly by the run-time system itself, usually
due to a triggered event. Functions that do special, pre-defined
-things include C<BEGIN>, C<CHECK>, C<INIT>, C<END>, C<AUTOLOAD>, and
-C<DESTROY>--plus all functions mentioned in L<perltie>.
+things include C<BEGIN>, C<CHECK>, C<INIT>, C<END>, C<AUTOLOAD>,
+C<CLONE> and C<DESTROY>--plus all functions mentioned in L<perltie>.
=head2 Private Variables via my()
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 $_ in any routine that assigns
to it. Look out for implicit assignments in C<while> conditionals.
-=item 2. You need to create a local file or directory handle or a local function.
+=item 2.
+
+You need to create a local file or directory handle or a local function.
A function that needs a filehandle of its own must use
C<local()> on a complete typeglob. This can be used to create new symbol
See L<perlref/"Function Templates"> for more about manipulating
functions by name in this way.
-=item 3. You want to temporarily change just one element of an array or hash.
+=item 3.
+
+You want to temporarily change just one element of an array or hash.
You can C<local>ize just one element of an aggregate. Usually this
is done on dynamics:
subroutine, then it behaves like an old-fashioned subroutine. It
naturally falls out from this rule that prototypes have no influence
on subroutine references like C<\&foo> or on indirect subroutine
-calls like C<&{$subref}> or C<$subref-E<gt>()>.
+calls like C<&{$subref}> or C<< $subref->() >>.
Method calls are not influenced by prototypes either, because the
function to be called is indeterminate at compile time, since
A subroutine declaration or definition may have a list of attributes
associated with it. If such an attribute list is present, it is
-broken up at space or comma boundaries and treated as though a
+broken up at space or colon boundaries and treated as though a
C<use attributes> had been seen. See L<attributes> for details
about what attributes are currently supported.
Unlike the limitation with the obsolescent C<use attrs>, the
Examples of valid syntax (even though the attributes are unknown):
- sub fnord (&\%) : switch(10,foo(7,3)) , , expensive ;
- sub plugh () : Ugly('\(") , Bad ;
+ sub fnord (&\%) : switch(10,foo(7,3)) : expensive ;
+ sub plugh () : Ugly('\(") :Bad ;
sub xyzzy : _5x5 { ... }
Examples of invalid syntax:
sub snoid : Ugly('(') ; # ()-string not balanced
sub xyzzy : 5x5 ; # "5x5" not a valid identifier
sub plugh : Y2::north ; # "Y2::north" not a simple identifier
- sub snurt : foo + bar ; # "+" not a comma or space
+ sub snurt : foo + bar ; # "+" not a colon or space
The attribute list is passed as a list of constant strings to the code
which associates them with the subroutine. In particular, the second example
See L<perlref/"Function Templates"> for more about references and closures.
See L<perlxs> if you'd like to learn about calling C subroutines from Perl.
-See L<perlembed> if you'd like to learn about calling PErl subroutines from C.
+See L<perlembed> if you'd like to learn about calling Perl subroutines from C.
See L<perlmod> to learn about bundling up your functions in separate files.
See L<perlmodlib> to learn what library modules come standard on your system.
See L<perltoot> to learn how to make object method calls.