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Importer-0.026
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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.

SYNOPSIS

# 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;

# Import symbols into variables
my $croak = Importer->get_one(Carp => qw/croak/);
$croak->("This will croak");

my $CARP = Importer->get(Carp => qw/croak confess cluck/);
$CARP->{croak}->("This will croak");
$CARP->{cluck}->("This will cluck");
$CARP->{confess}->("This will confess");

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.

COMPATIBILITY

This module aims for 100% compatibility 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, \&SET_SYMBOL, @SYMBOLS;

SUPPORTED FEATURES

TAGS

You can define/import subsets of symbols using predefined tags.

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

Importer will automatically populate the :DEFAULT tag for you. Importer will also give you an :ALL tag with ALL exports so long as the exporter does not define a :ALL tag already.

/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/;

EXCLUDING SYMBOLS

You can exclude 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

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_' },
);

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.

CUSTOM EXPORT ASSIGNMENT

This lets you provide an alternative to the *name = $ref export assignment. See the list of parameters to import()

UNIMPORTING

See "UNIMPORT PARAMETERS".

ANONYMOUS EXPORTS

See "%EXPORT_ANON".

GENERATED EXPORTS

See "%EXPORT_GEN".

UNIMPORT PARAMETERS

no Importer;    # Remove all subs 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.

SUPPORTED VARIABLES

@EXPORT

This is used exactly the way Exporter uses it.

List of symbols to export. Sigil is optional for subs. Symbols listed here are exported by default. If possible you should put symbols in @EXPORT_OK instead.

our @EXPORT = qw/foo bar &baz $BAT/;

@EXPORT_OK

This is used exactly the way Exporter uses it.

List of symbols that can be imported. Sigil is optional for subs. Symbols listed here are not exported by default. This is preferred over @EXPORT.

our @EXPORT_OK = qw/foo bar &baz $BAT/;

%EXPORT_TAGS

This module supports tags exactly the way Exporter does.

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

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

Tags can be specified this way:

our %EXPORT_TAGS = (
    oos => [qw/foo boo zoo/],
    ees => [qw/fee bee zee/],
);

@EXPORT_FAIL

This is used exactly the way Exporter uses it.

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 for documentation of this feature.

our @EXPORT_FAIL = qw/maybe_bad/;

%EXPORT_ANON

This is new to this module, Exporter does not support it.

This allows you to export symbols that are not actually in your package symbol table. The keys should be the symbol names, the values are the references for the symbols.

our %EXPORT_ANON = (
    '&foo' => sub { 'foo' }
    '$foo' => \$foo,
    ...
);

%EXPORT_GEN

This is new to this module, Exporter does not support it.

This allows you to export symbols that are generated on export. The key should be the name of a symbol. The value should be a coderef that produces a reference that will be exported.

When the generators are called they will receive 2 arguments, the package the symbol is being exported into, and the symbol being imported (name may or may not include sigil for subs).

our %EXPORT_GEN = (
    '&foo' => sub {
        my $from_package = shift;
        my ($into_package, $symbol_name) = @_;
        ...
        return sub { ... };
    },
    ...
);

%EXPORT_MAGIC

This is new to this module. Exporter does not support it.

This allows you to define custom actions to run AFTER an export has been injected into the consumers namespace. This is a good place to enable parser hooks like with Devel::Declare. These will NOT be run if a consumer uses a custom assignment callback.

our %EXPORT_MAGIC = (
    foo => sub {
        my $from = shift;    # Should be the package doing the exporting
        my %args = @_;

        my $into      = $args{into};         # Package symbol was exported into
        my $orig_name = $args{orig_name};    # Original name of the export (in the exporter)
        my $new_name  = $args{new_name};     # Name the symbol was imported as
        my $ref       = $args{ref};          # The reference to the symbol

        ...; # whatever you want, return is ignored.
    },
);

CLASS METHODS

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. IMPORTER_MENU() must be defined in your package, not a base class!

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
        export_anon  => \%EXPORT_ANON,     # Anonymous symbols to export
        export_magic => \%EXPORT_MAGIC,    # Magic to apply after a symbol is exported

        generate   => \&GENERATE,          # Sub to generate dynamic exports
                                           # OR
        export_gen => \%EXPORT_GEN,        # Hash of builders, key is symbol
                                           # name, value is sub that generates
                                           # the symbol ref.
    );
}

sub GENERATE {
    my ($symbol) = @_;

    ...

    return $ref;
}

All exports must be listed in either @EXPORT or @EXPORT_OK, or be keys in %EXPORT_GEN or %EXPORT_ANON to be allowed. 'export_tags', 'export_fail', 'export_anon', 'export_gen', and 'generate' are optional. You cannot combine 'generate' and 'export_gen'.

Note: If your GENERATE sub needs the $class, $into, or $caller then your IMPORTER_MENU() method will need to build an anonymous sub that closes over them:

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

    return (
        ...
        generate => sub { $class->GENERATE($into, $caller, @_) },
    );
}

OO Interface

use Importer;

my $imp = Importer->new(from => 'Some::Exporter');

$imp->do_import('Destination::Package');
$imp->do_import('Another::Destination', @symbols);

Or, maybe more useful:

my $imp = Importer->new(from => 'Carp');
my $croak = $imp->get_one('croak');
$croak->("This will croak");

OBJECT CONSTRUCTION

OBJECT METHODS

FUNCTIONS

These can be imported:

use Importer 'Importer' => qw/import optimal_import/;

SOURCE

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

MAINTAINERS

AUTHORS

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/