1if(3pm)                Perl Programmers Reference Guide                if(3pm)
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NAME

6       if - "use" a Perl module if a condition holds
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SYNOPSIS

9           use if CONDITION, "MODULE", ARGUMENTS;
10           no  if CONDITION, "MODULE", ARGUMENTS;
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DESCRIPTION

13   "use if"
14       The "if" module is used to conditionally load another module.  The
15       construct:
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17           use if CONDITION, "MODULE", ARGUMENTS;
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19       ... will load "MODULE" only if "CONDITION" evaluates to true; it has no
20       effect if "CONDITION" evaluates to false.  (The module name, assuming
21       it contains at least one "::", must be quoted when 'use strict "subs";'
22       is in effect.)  If the CONDITION does evaluate to true, then the above
23       line has the same effect as:
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25           use MODULE ARGUMENTS;
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27       For example, the Unicode::UCD module's charinfo function will use two
28       functions from Unicode::Normalize only if a certain condition is met:
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30           use if defined &DynaLoader::boot_DynaLoader,
31               "Unicode::Normalize" => qw(getCombinClass NFD);
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33       Suppose you wanted "ARGUMENTS" to be an empty list, i.e., to have the
34       effect of:
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36           use MODULE ();
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38       You can't do this with the "if" pragma; however, you can achieve
39       exactly this effect, at compile time, with:
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41           BEGIN { require MODULE if CONDITION }
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43   "no if"
44       The "no if" construct is mainly used to deactivate categories of
45       warnings when those categories would produce superfluous output under
46       specified versions of perl.
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48       For example, the "redundant" category of warnings was introduced in
49       Perl-5.22.  This warning flags certain instances of superfluous
50       arguments to "printf" and "sprintf".  But if your code was running
51       warnings-free on earlier versions of perl and you don't care about
52       "redundant" warnings in more recent versions, you can call:
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54           use warnings;
55           no if $] >= 5.022, q|warnings|, qw(redundant);
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57           my $test    = { fmt  => "%s", args => [ qw( x y ) ] };
58           my $result  = sprintf $test->{fmt}, @{$test->{args}};
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60       The "no if" construct assumes that a module or pragma has correctly
61       implemented an "unimport()" method -- but most modules and pragmata
62       have not.  That explains why the "no if" construct is of limited
63       applicability.
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BUGS

66       The current implementation does not allow specification of the required
67       version of the module.
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SEE ALSO

70       Module::Requires can be used to conditionally load one or modules, with
71       constraints based on the version of the module.  Unlike "if" though,
72       Module::Requires is not a core module.
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74       Module::Load::Conditional provides a number of functions you can use to
75       query what modules are available, and then load one or more of them at
76       runtime.
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78       The provide module from CPAN can be used to select one of several
79       possible modules to load based on the version of Perl that is running.
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AUTHOR

82       Ilya Zakharevich <mailto:ilyaz@cpan.org>.
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85       This software is copyright (c) 2002 by Ilya Zakharevich.
86
87       This is free software; you can redistribute it and/or modify it under
88       the same terms as the Perl 5 programming language system itself.
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92perl v5.30.2                      2020-03-27                           if(3pm)
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