NAME

Importer - Alternative but compatible interface to modules that export symbols.

DESCRIPTION

This module acts as a layer between Exporter and modules which consume exports. It is feature-compatible with Exporter, plus some much needed extras. You can use this to import symbols from any exporter that follows Exporters specification. The exporter modules themselves do not need to use or inherit from the Exporter module, they just need to set @EXPORT and/or other variables.

*** EXPERIMENTAL ***

This module is still experimental. Anything can change at any time. Testing is currently VERY insufficient.

SYNOPSYS

    # Import defaults
    use Importer 'Some::Module';

    # Import a list
    use Importer 'Another::Module' => qw/foo bar baz/;

    # Import a specific version:
    use Importer 'That::Module' => '1.00';

    # Require a sepcific version of Importer
    use Importer 0.001, 'Foo::Bar' => qw/a b c/;

    foo()
    bar()
    baz()

    # Remove all subroutines imported by Importer
    no Importer;

WHY?

There was recently a discussion on p5p about adding features to Exporter. This conversation raised some significant concerns, those are listed here, in addition to others.

The burden is on export consumers to specify a version of Exporter

Adding a feature to Exporter means that any consumer module that relies on the new features must depend on a specific version of Exporter. This seems somewhat backwords since Exporter is used by the module you are importing from.

Exporter.pm is really old/crazy code

Not much more to say here. It is very old, it is very crazy, and if you break it you break EVERYTHING.

Using a modules import() for exporting makes it hard to give it other purposes

It is not unusual for a module to want to export symbols and prvide import behaviors. It is also not unusual for a consumer to only want 1 or the other. Using this module you can import symbols without also getting the import() side effects.

In addition, moving forward, modules can specify exports and have a custom import() without conflating the two. A module can tell you to use Importer to get the symbols, and to use the module directly for behaviors. A module could also use Importer within its own import() method without the need to subclass Exporter, or bring in its import() method.

There are other exporter modules on cpan

This module normally assumes an Exporter uses Exporter, so it looks for the variables and method Exporter expects. However, other exporters on cpan can override this using the IMPORTER_MENU() hook.

COMPATABILITY

This module aims for 100% compatabilty with every feature of Exporter, plus added features such as import renaming.

If you find something that works differently, or not at all when compared to Exporter please report it as a bug, unless it is noted as an intentional feature (like import renaming).

IMPORT PARAMETERS

    use Importer $IMPORTER_VERSION, $FROM_MODULE, $FROM_MODULE_VERSION, @SYMBOLS;

$IMPORTER_VERSION (optional)

If you provide a numeric argument as the first argument it will be treated as a version number. Importer will d a version check to make sure it is at least at the requested version.

$FROM_MODULE (required)

This is the only required argument. This is the name of the module to import symbols from.

$FROM_MODULE_VERSION (optional)

Any numeric argument following the $FROM_MODULE will be treated as a version check against $FROM_MODULE.

@SYMBOLS (optional)

Symbols you wish to import. If no symbols are specified then the defaults will be used.

SUPPORTED FEATURES

RENAMING SYMBOLS AT IMPORT

This is a new feature, Exporter does not support this on its own.

You can rename symbols at import time using a specification hash following the import name:

    use Importer 'Some::Thing' => (
        foo => { -as => 'my_foo' },
    );

You can also add a prefix and/or postfix:

    use Importer 'Some::Thing' => (
        foo => { -prefix => 'my_foo' },
    );

Using this syntax to set prefix and/or postfix also works on tags and patterns that are specified for import, in which case the prefix/postfix is applied to all symbols from the tag/patterm.

@EXPORT_FAIL

Use this to list subs that are not available on all platforms. If someone tries to import one of these, Importer will hit your $from-export_fail(@items) > callback to try to resolve the issue. See Exporter.pm for documentation of this feature.

%EXPORT_TAGS

This module supports tags exactly the way Exporter does.

    use Importer 'Some::Thing'  => ':DEFAULT';

    use Importer 'Other::Thing' => ':some_tag';

/PATTERN/ or qr/PATTERN/

You can import all symbols that match a pattern. The pattern can be supplied a string starting and ending with '/', or you can provide a qr/../ reference.

    use Importer 'Some::Thing' => '/oo/';

    use Importer 'Some::Thing' => qr/oo/;

EXLUDING SYMBOLS

You can exlude symbols by prefixing them with '!'.

    use Importer 'Some::Thing'
        '!foo',         # Exclude one specific symbol
        '!/pattern/',   # Exclude all matching symbols
        '!' => qr/oo/,  # Exclude all that match the following arg
        '!:tag';        # Exclude all in tag

UNIMPORT PARAMETERS

    no Importer;    # Remove all sub brought in with Importer

    no Importer qw/foo bar/;    # Remove only the specified subs

Only subs can be unimported.

You can only unimport subs imported using Importer.

CLASS METHODS

Importer->import($from)

Importer->import($from, $version)

Importer->import($from, @imports)

Importer->import($from, $from_version, @imports)

Importer->import($importer_version, $from, ...)

This is the magic behind use Importer ....

Importer->import_into($from, $into, @imports)

Importer->import_into($from, $level, @imports)

You can use this to import symbols from $from into $into. $into may either be a package name, or a caller level to get the name from.

Importer->unimport()

Importer->unimport(@sub_name)

This is the magic behind no Importer ....

Importer->unimport_from($from, @sub_names)

Importer->unimport_from($level, @sub_names)

This lets you remove imported symbols from $from. $from my be a package name, or a caller level.

USING WITH OTHER EXPORTER IMPLEMENTATIONS

If you want your module to work with Importer, but you use something other than Exporter to define your exports, you can make it work be defining the IMPORTER_MENU method in your package. As well other exporters can be updated to support Importer by putting this sub in your package:

    sub IMPORTER_MENU {
        my $class = shift;
        my ($into, $caller) = @_;

        return (
            export      => \@EXPORT,      # Default exports
            export_ok   => \@EXPORT_OK,   # Other allowed exports
            export_tags => \%EXPORT_TAGS, # Define tags
            export_fail => \@EXPORT_FAIL, # For subs that may not always be available
            generate    => \&GENERATE,    # Sub to generate dynamic exports
        );
    }

    sub GENERATE {
        my $class = shift;

        my ($symbol) = @_;

        ...

        return $ref;
    }

All exports must be listed in either @EXPORT or @EXPORT_OK to be allowed. %EXPORT_TAGS, @EXPORT_FAIL, and \&GENERATE are optional.

SOURCE

The source code repository for symbol can be found at http://github.com/exodist/Importer.

MAINTAINERS

Chad Granum <exodist@cpan.org>

AUTHORS

Chad Granum <exodist@cpan.org>

COPYRIGHT

Copyright 2015 Chad Granum <exodist7@gmail.com>.

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

See http://dev.perl.org/licenses/

cpanm Importer

perl -MCPAN -e shell
install Importer