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Daniel Muey
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NAME

Module::Want - Check @INC once for modules that you want but may not have

VERSION

This document describes Module::Want version 0.6

SYNOPSIS

    use Module::Want;

    if (have_mod('Encode')) {
        ... use Encode::whatever ...
    }
    else {
        ... use Encode:: alternative ...
    }

DESCRIPTION

Sometimes you want to lazy load a module for use in, say, a loop or function. First you do the eval-require but then realize if the module is not available it will re-search @INC each time. So then you add a lexical boolean to your eval and do the same simple logic all over the place. On and on it goes :)

This module encapsulates that logic so that have_mod() is like eval { require X; 1 } but if the module can't be loaded it will remember that fact and not look in @INC again on subsequent calls.

For example, this searches @INC for X.pm every iteration of the loop:

    while( ... ) {
        if (eval { require X; 1 }) {
            ... use X code ...
        }
        else {
            ... do X-alternative code ...
        }
    }

This searches @INC for X.pm once:

    while( ... ) {
        if (have_mod('X')) {
            ... use X code ...
        }
        else {
            ... do X-alternative code ...
        }
    }

Additionally, it will not trip the sig die handler. That prevents a benign eval from tripping a potentially fatal sig handler. (i.e. another step you'd have to do manually with the straight eval form.)

INTERFACE

import() puts have_mod() into the caller's name space.

have_mod()

Takes the name space to require() if we have not tried already.

Returns true if it could be loaded. False otherwise.

You can give it a second true argument to skip using the value from the last time it was called and re-try require()ing it.

   if (!have_mod('X')) {
       # do some things to try and ger X available 
   }
   
   if (have_mod('X',1)) {
       # sweet we have it now!
   }

import()

You can use() it with a list to call have_mod() on:

   use Module::Want qw(X Y Z); # calls have_mod('X'), have_mod('Y'), and have_mod('Z')

Utility functions

These aren't the real reasons for this module but they've proven useful when you're doing things that would require have_mod() so here they are:

They can all be exported thusly:

    use Module::Want qw(is_ns);

For an entire suite if name space utilities see Module::Util and friends.

is_ns($ns)

Boolean of if '$ns' is a proper name space or not.

    if(is_ns($ns)) {
        ... use $ns as a module/class name ...
    }
    else {
       ... "invalid input please try again" prompt ...
    }

get_ns_regexp()

Returns a quoted Regexp that matches a name space for use in your regexes.

get_all_use_require_in_text($text)

This will return a list of all name spaces being use()d or require()d in perlish looking $text.

It will also return ones being eval()d in.

It is very simplistic (e.g. it may or may not return use/require statements that are in comments, it will match verbiage in a here doc that start w/ “use”) so if it does not fit your needs you'll need to try a PPI based solution (I have Perl::DependList on my radar that does just that.).

get_inc_key($ns)

Returns what $ns's key in %INC would be (if is_ns($ns) of course)

    if (my $inc_key =  get_inc_key($ns)) {
        if (exists $INC{$inc_key}) {
           ... in %INC ...
        }
        else {
            ... not in %INC ...
        }    
    }

%INC keys are always unix format so don't panic

If I've been misinformed of that fact then please let me know, thanks

get_relative_path_of_ns($ns)

Alias of "get_inc_key($ns)" whose name indicates a different intent.

get_clean_ns($ns)

Takes $ns, trims leading and trailing whitespace and turns ' into ::, and returns the cleaned copy.

normalize_ns($ns)

Alias of "get_clean_ns($ns)" whose name indicates a different intent.

ns2distname($ns)

Turns the given name space into a distribution name.

e.g. Foo::Bar::Baz becomes Foo-Bar-Baz

distname2ns($distname)

Turns the given distribution name into a name space.

e.g. Foo-Bar-Baz becomes Foo::Bar::Baz

get_inc_path_via_have_mod($ns)

Return the %INC entry’s value if we have_mod($ns);

search_inc_paths($ns)

Without loading the module, search for $ns in @INC.

In scalar context returns the first path it is found in, in list context returns all paths it is found in.

    my $first_path_it_is_in = search_inc_paths($ns);
    my @all_paths_it_is_in  = search_inc_paths($ns);

By default it returns the path it is in without the module-name part of the path. A second true argument will return the entire path.

    my $abs_path_of_pm_file = search_inc_paths($ns,1);

DIAGNOSTICS

Invalid Namespace

The argument to have_mod() is not a name space

CONFIGURATION AND ENVIRONMENT

Module::Want requires no configuration files or environment variables.

DEPENDENCIES

None.

INCOMPATIBILITIES

None reported.

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to bug-module-want@rt.cpan.org, or through the web interface at http://rt.cpan.org.

AUTHOR

Daniel Muey <http://drmuey.com/cpan_contact.pl>

LICENCE AND COPYRIGHT

Copyright (c) 2010, Daniel Muey <http://drmuey.com/cpan_contact.pl>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.