if - phpMan

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.