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package if; $VERSION = '0.0606'; sub work { my $method = shift() ? 'import' : 'unimport'; unless (@_ >= 2) { my $type = ($method eq 'import') ? 'use' : 'no'; die "Too few arguments to '$type if' (some code returning an empty list in list context?)" } return unless shift; # CONDITION my $p = $_[0]; # PACKAGE (my $file = "$p.pm") =~ s!::!/!g; require $file; # Works even if $_[0] is a keyword (like open) my $m = $p->can($method); goto &$m if $m; } sub import { shift; unshift @_, 1; goto &work } sub unimport { shift; unshift @_, 0; goto &work } 1; __END__ =head1 NAME if - C a Perl module if a condition holds (also can C a module) =head1 SYNOPSIS use if CONDITION, MODULE => ARGUMENTS; no if CONDITION, MODULE => ARGUMENTS; =head1 DESCRIPTION The C module is used to conditionally load or unload another module. The construct use if CONDITION, MODULE => ARGUMENTS; will load MODULE only if CONDITION evaluates to true. The above statement has no effect unless C 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<< => >> above provides necessary quoting of C. 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: use if $^O ne 'MSWin32', POSIX => qw/setlocale LC_ALL/; If run on any operating system other than Windows, this will import the functions C and C from L. On Windows it does nothing. The following is used to L core modules beyond a certain version of Perl: use if $] > 5.016, 'deprecate'; This line is taken from L 3.04, and marks it as deprecated beyond Perl 5.16. If you C in Perl 5.18, for example, and you have used L, then you'll get a warning message (the deprecate module looks to see whether the calling module was C'd from a core library directory, and if so, generates a warning), unless you've installed a more recent version of L from CPAN. You can also specify to NOT use something: no if $] ge 5.021_006, warnings => "locale"; This warning category was added in the specified Perl version (a development release). Without the C<'if'>, 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 can be used to conditionally load one or modules, with constraints based on the version of the module. Unlike C though, L is not a core module. L 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 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. =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