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author | Norbert Preining <norbert@preining.info> | 2019-09-02 13:46:59 +0900 |
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committer | Norbert Preining <norbert@preining.info> | 2019-09-02 13:46:59 +0900 |
commit | e0c6872cf40896c7be36b11dcc744620f10adf1d (patch) | |
tree | 60335e10d2f4354b0674ec22d7b53f0f8abee672 /systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm |
Initial commit
Diffstat (limited to 'systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm')
-rw-r--r-- | systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm b/systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm new file mode 100644 index 0000000000..166de7bb10 --- /dev/null +++ b/systems/texlive/tlnet/tlpkg/tlperl/lib/if.pm @@ -0,0 +1,116 @@ +package if; + +$VERSION = '0.0608'; + +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<use> a Perl module if a condition holds + +=head1 SYNOPSIS + + use if CONDITION, "MODULE", ARGUMENTS; + no if CONDITION, "MODULE", ARGUMENTS; + +=head1 DESCRIPTION + +=head2 C<use if> + +The C<if> module is used to conditionally load another module. The construct: + + use if CONDITION, "MODULE", ARGUMENTS; + +... will load C<MODULE> only if C<CONDITION> evaluates to true; it has no +effect if C<CONDITION> evaluates to false. (The module name, assuming it +contains at least one C<::>, must be quoted when C<'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 F<Unicode::UCD> module's F<charinfo> function will use two functions from F<Unicode::Normalize> only if a certain condition is met: + + use if defined &DynaLoader::boot_DynaLoader, + "Unicode::Normalize" => qw(getCombinClass NFD); + +Suppose you wanted C<ARGUMENTS> to be an empty list, I<i.e.>, to have the +effect of: + + use MODULE (); + +You can't do this with the C<if> pragma; however, you can achieve +exactly this effect, at compile time, with: + + BEGIN { require MODULE if CONDITION } + +=head2 C<no if> + +The C<no if> construct is mainly used to deactivate categories of warnings +when those categories would produce superfluous output under specified +versions of F<perl>. + +For example, the C<redundant> category of warnings was introduced in +Perl-5.22. This warning flags certain instances of superfluous arguments to +C<printf> and C<sprintf>. But if your code was running warnings-free on +earlier versions of F<perl> and you don't care about C<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 C<no if> construct assumes that a module or pragma has correctly +implemented an C<unimport()> method -- but most modules and pragmata have not. +That explains why the C<no if> construct is of limited applicability. + +=head1 BUGS + +The current implementation does not allow specification of the required +version of the module. + +=head1 SEE ALSO + +L<Module::Requires> can be used to conditionally load one or modules, +with constraints based on the version of the module. +Unlike C<if> though, L<Module::Requires> is not a core module. + +L<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 L<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. + +=head1 AUTHOR + +Ilya Zakharevich L<mailto:ilyaz@cpan.org>. + +=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 |