phpman > man > if(3perl)

NAME
    if - "use" a Perl module if a condition holds

SYNOPSIS
        use if CONDITION, "MODULE", ARGUMENTS;
        no  if CONDITION, "MODULE", ARGUMENTS;

DESCRIPTION
  "use if"
    The "if" module is used to conditionally load another module. The construct:

        use if CONDITION, "MODULE", ARGUMENTS;

    ... will load "MODULE" only if "CONDITION" evaluates to true; it has no effect if "CONDITION"
    evaluates to false. (The module name, assuming it contains at least one "::", must be quoted
    when 'use strict "subs";' is in effect.) If the CONDITION does evaluate to true, then the above
    line has the same effect as:

        use MODULE ARGUMENTS;

    For example, the Unicode::UCD module's charinfo function will use two functions from
    Unicode::Normalize only if a certain condition is met:

        use if defined &DynaLoader::boot_DynaLoader,
            "Unicode::Normalize" => qw(getCombinClass NFD);

    Suppose you wanted "ARGUMENTS" to be an empty list, *i.e.*, to have the effect of:

        use MODULE ();

    You can't do this with the "if" pragma; however, you can achieve exactly this effect, at compile
    time, with:

        BEGIN { require MODULE if CONDITION }

  "no if"
    The "no if" construct is mainly used to deactivate categories of warnings when those categories
    would produce superfluous output under specified versions of perl.

    For example, the "redundant" category of warnings was introduced in Perl-5.22. This warning
    flags certain instances of superfluous arguments to "printf" and "sprintf". But if your code was
    running warnings-free on earlier versions of perl and you don't care about "redundant" warnings
    in more recent versions, you can call:

        use warnings;
        no if $] >= 5.022, q|warnings|, qw(redundant);

        my $test    = { fmt  => "%s", args => [ qw( x y ) ] };
        my $result  = sprintf $test->{fmt}, @{$test->{args}};

    The "no if" construct assumes that a module or pragma has correctly implemented an "unimport()"
    method -- but most modules and pragmata have not. That explains why the "no if" construct is of
    limited applicability.

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

SEE ALSO
    Module::Requires can be used to conditionally load one or modules, with constraints based on the
    version of the module. Unlike "if" though, Module::Requires is not a core module.

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

    The provide module from CPAN can be used to select one of several possible modules to load based
    on the version of Perl that is running.

AUTHOR
    Ilya Zakharevich <mailto:ilyaz AT cpan.org>.

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.