<h2>Editing File: /usr/share/perl5/if.pm</h2><form method='post'><textarea name='content' class='file-edit'>package if;

$VERSION = '0.0606';

sub work {
  my $method = shift() ? 'import' : 'unimport';
  unless (@_ &gt;= 2) {
    my $type = ($method eq 'import') ? 'use' : 'no';
    die &quot;Too few arguments to '$type if' (some code returning an empty list in list context?)&quot;
  }
  return unless shift;		# CONDITION

  my $p = $_[0];		# PACKAGE
  (my $file = &quot;$p.pm&quot;) =~ s!::!/!g;
  require $file;		# Works even if $_[0] is a keyword (like open)
  my $m = $p-&gt;can($method);
  goto &amp;$m if $m;
}

sub import   { shift; unshift @_, 1; goto &amp;work }
sub unimport { shift; unshift @_, 0; goto &amp;work }

1;
__END__

=head1 NAME

if - C&lt;use&gt; a Perl module if a condition holds (also can C&lt;no&gt; a module)

=head1 SYNOPSIS

  use if CONDITION, MODULE =&gt; ARGUMENTS;
  no if CONDITION, MODULE =&gt; ARGUMENTS;

=head1 DESCRIPTION

The C&lt;if&gt; module is used to conditionally load or unload another module.
The construct

  use if CONDITION, MODULE =&gt; ARGUMENTS;

will load MODULE only if CONDITION evaluates to true.
The above statement has no effect unless C&lt;CONDITION&gt; is true.
If the CONDITION does evaluate to true, then the above line has
the same effect as:

  use MODULE ARGUMENTS;

The use of C&lt;&lt; =&gt; &gt;&gt; above provides necessary quoting of C&lt;MODULE&gt;.
If you don't use the fat comma (eg you don't have any ARGUMENTS),
then you'll need to quote the MODULE.

=head2 EXAMPLES

The following line is taken from the testsuite for L&lt;File::Map&gt;:

  use if $^O ne 'MSWin32', POSIX =&gt; qw/setlocale LC_ALL/;

If run on any operating system other than Windows,
this will import the functions C&lt;setlocale&gt; and C&lt;LC_ALL&gt; from L&lt;POSIX&gt;.
On Windows it does nothing.

The following is used to L&lt;deprecate&gt; core modules beyond a certain version of Perl:

  use if $] &gt; 5.016, 'deprecate';

This line is taken from L&lt;Text::Soundex&gt; 3.04,
and marks it as deprecated beyond Perl 5.16.
If you C&lt;use Text::Soundex&gt; in Perl 5.18, for example,
and you have used L&lt;warnings&gt;,
then you'll get a warning message
(the deprecate module looks to see whether the
calling module was C&lt;use&gt;'d from a core library directory,
and if so, generates a warning),
unless you've installed a more recent version of L&lt;Text::Soundex&gt; from CPAN.

You can also specify to NOT use something:

 no if $] ge 5.021_006, warnings =&gt; &quot;locale&quot;;

This warning category was added in the specified Perl version (a development
release).  Without the C&lt;'if'&gt;, trying to use it in an earlier release would
generate an unknown warning category error.

=head1 BUGS

The current implementation does not allow specification of the
required version of the module.

=head1 SEE ALSO

L&lt;Module::Requires&gt; can be used to conditionally load one or modules,
with constraints based on the version of the module.
Unlike C&lt;if&gt; though, L&lt;Module::Requires&gt; is not a core module.

L&lt;Module::Load::Conditional&gt; provides a number of functions you can use to
query what modules are available, and then load one or more of them at runtime.

L&lt;provide&gt; can be used to select one of several possible modules to load,
based on what version of Perl is running.

=head1 AUTHOR

Ilya Zakharevich L&lt;mailto:ilyaz@cpan.org&gt;.

=head1 COPYRIGHT AND LICENCE

This software is copyright (c) 2002 by Ilya Zakharevich.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
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