exporter.pm

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

package Exporter;

require 5.006;

# Be lean.
#use strict;
#no strict 'refs';

our $Debug = 0;
our $ExportLevel = 0;
our $Verbose ||= 0;
our $VERSION = '5.62';
our (%Cache);
# Carp does this now for us, so we can finally live w/o Carp
#$Carp::Internal{Exporter} = 1;

sub as_heavy {
  require Exporter::Heavy;
  # Unfortunately, this does not work if the caller is aliased as *name = \&foo
  # Thus the need to create a lot of identical subroutines
  my $c = (caller(1))[3];
  $c =~ s/.*:://;
  \&{"Exporter::Heavy::heavy_$c"};
}

sub export {
  goto &{as_heavy()};
}

sub import {
  my $pkg = shift;
  my $callpkg = caller($ExportLevel);

  if ($pkg eq "Exporter" and @_ and $_[0] eq "import") {
    *{$callpkg."::import"} = \&import;
    return;
  }

  # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
  my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"});
  return export $pkg, $callpkg, @_
    if $Verbose or $Debug or @$fail > 1;
  my $export_cache = ($Cache{$pkg} ||= {});
  my $args = @_ or @_ = @$exports;

  local $_;
  if ($args and not %$export_cache) {
    s/^&//, $export_cache->{$_} = 1
      foreach (@$exports, @{"$pkg\::EXPORT_OK"});
  }
  my $heavy;
  # Try very hard not to use {} and hence have to  enter scope on the foreach
  # We bomb out of the loop with last as soon as heavy is set.
  if ($args or $fail) {
    ($heavy = (/\W/ or $args and not exists $export_cache->{$_}
               or @$fail and $_ eq $fail->[0])) and last
                 foreach (@_);
  } else {
    ($heavy = /\W/) and last
      foreach (@_);
  }
  return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
  local $SIG{__WARN__} = 
	sub {require Carp; &Carp::carp};
  # shortcut for the common case of no type character
  *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
}

# Default methods

sub export_fail {
    my $self = shift;
    @_;
}

# Unfortunately, caller(1)[3] "does not work" if the caller is aliased as
# *name = \&foo.  Thus the need to create a lot of identical subroutines
# Otherwise we could have aliased them to export().

sub export_to_level {
  goto &{as_heavy()};
}

sub export_tags {
  goto &{as_heavy()};
}

sub export_ok_tags {
  goto &{as_heavy()};
}

sub require_version {
  goto &{as_heavy()};
}

1;
__END__

=head1 NAME

Exporter - Implements default import method for modules

=head1 SYNOPSIS

In module YourModule.pm:

  package YourModule;
  require Exporter;
  @ISA = qw(Exporter);
  @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request

or

  package YourModule;
  use Exporter 'import'; # gives you Exporter's import() method directly
  @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request

In other files which wish to use YourModule:

  use ModuleName qw(frobnicate);      # import listed symbols
  frobnicate ($left, $right)          # calls YourModule::frobnicate

Take a look at L</Good Practices> for some variants
you will like to use in modern Perl code.

=head1 DESCRIPTION

The Exporter module implements an C<import> method which allows a module
to export functions and variables to its users' namespaces. Many modules
use Exporter rather than implementing their own C<import> method because
Exporter provides a highly flexible interface, with an implementation optimised
for the common case.

Perl automatically calls the C<import> method when processing a
C<use> statement for a module. Modules and C<use> are documented
in L<perlfunc> and L<perlmod>. Understanding the concept of
modules and how the C<use> statement operates is important to
understanding the Exporter.

=head2 How to Export

The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
symbols that are going to be exported into the users name space by
default, or which they can request to be exported, respectively.  The
symbols can represent functions, scalars, arrays, hashes, or typeglobs.
The symbols must be given by full name with the exception that the
ampersand in front of a function is optional, e.g.

    @EXPORT    = qw(afunc $scalar @array);   # afunc is a function
    @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc

If you are only exporting function names it is recommended to omit the
ampersand, as the implementation is faster this way.

=head2 Selecting What To Export

Do B<not> export method names!

Do B<not> export anything else by default without a good reason!

Exports pollute the namespace of the module user.  If you must export
try to use @EXPORT_OK in preference to @EXPORT and avoid short or
common symbol names to reduce the risk of name clashes.

Generally anything not exported is still accessible from outside the
module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
syntax.  By convention you can use a leading underscore on names to
informally indicate that they are 'internal' and not for public use.

(It is actually possible to get private functions by saying:

  my $subref = sub { ... };
  $subref->(@args);            # Call it as a function
  $obj->$subref(@args);        # Use it as a method

However if you use them for methods it is up to you to figure out
how to make inheritance work.)

As a general rule, if the module is trying to be object oriented
then export nothing. If it's just a collection of functions then
@EXPORT_OK anything but use @EXPORT with caution. For function and
method names use barewords in preference to names prefixed with
ampersands for the export lists.

Other module design guidelines can be found in L<perlmod>.

=head2 How to Import

In other files which wish to use your module there are three basic ways for
them to load your module and import its symbols:

=over 4

=item C<use ModuleName;>

This imports all the symbols from ModuleName's @EXPORT into the namespace
of the C<use> statement.

=item C<use ModuleName ();>

This causes perl to load your module but does not import any symbols.

=item C<use ModuleName qw(...);>

This imports only the symbols listed by the caller into their namespace.
All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error
occurs. The advanced export features of Exporter are accessed like this,
but with list entries that are syntactically distinct from symbol names.

=back

Unless you want to use its advanced features, this is probably all you
need to know to use Exporter.

=head1 Advanced features

=head2 Specialised Import Lists

If any of the entries in an import list begins with !, : or / then
the list is treated as a series of specifications which either add to
or delete from the list of names to import. They are processed left to
right. Specifications are in the form:

    [!]name         This name only
    [!]:DEFAULT     All names in @EXPORT
    [!]:tag         All names in $EXPORT_TAGS{tag} anonymous list
    [!]/pattern/    All names in @EXPORT and @EXPORT_OK which match

A leading ! indicates that matching names should be deleted from the
list of names to import.  If the first specification is a deletion it
is treated as though preceded by :DEFAULT. If you just want to import
extra names in addition to the default set you will still need to
include :DEFAULT explicitly.

e.g., Module.pm defines:

    @EXPORT      = qw(A1 A2 A3 A4 A5);
    @EXPORT_OK   = qw(B1 B2 B3 B4 B5);
    %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);

    Note that you cannot use tags in @EXPORT or @EXPORT_OK.
    Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.

An application using Module can say something like:

    use Module qw(:DEFAULT :T2 !B3 A3);

Other examples include:

    use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
    use POSIX  qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);

Remember that most patterns (using //) will need to be anchored
with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.

You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
specifications are being processed and what is actually being imported
into modules.

=head2 Exporting without using Exporter's import method

Exporter has a special method, 'export_to_level' which is used in situations
where you can't directly call Exporter's import method. The export_to_level
method looks like:

    MyPackage->export_to_level($where_to_export, $package, @what_to_export);

where $where_to_export is an integer telling how far up the calling stack
to export your symbols, and @what_to_export is an array telling what
symbols *to* export (usually this is @_).  The $package argument is
currently unused.

For example, suppose that you have a module, A, which already has an
import function:

    package A;

    @ISA = qw(Exporter);
    @EXPORT_OK = qw ($b);

    sub import
    {
	$A::b = 1;     # not a very useful import method
    }

and you want to Export symbol $A::b back to the module that called 
package A. Since Exporter relies on the import method to work, via 
inheritance, as it stands Exporter::import() will never get called. 
Instead, say the following:

    package A;
    @ISA = qw(Exporter);