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.

   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 backwards 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 provide
     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 methods Exporter expects. However, other
     exporters on cpan can override this using the IMPORTER_MENU() hook.

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;

   $IMPORTER_VERSION (optional)

     If you provide a numeric argument as the first argument it will be
     treated as a version number. Importer will do 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.

   \&SET_SYMBOL (optional)

     Normally Importer will put the exports into your namespace. This is
     usually done via a more complex form of *name = $ref. If you do NOT
     want this to happen then you can provide a custom sub to handle the
     assignment.

     This is an example that uses this feature to put all the exports into
     a lexical hash instead of modifying the namespace (This is how the
     get() method is implemented).

         my %CARP;
         use Importer Carp => sub {
             my ($name, $ref) = @_;
             $CARP{$name} = $ref;
         };

         $CARP{cluck}->("This will cluck");
         $CARP{croak}->("This will croak");

     The first two arguments to the custom sub are the name (no sigil),
     and the reference. The additional arguments are key/value pairs:

         sub set_symbol {
             my ($name, $ref, %info) = @_;
         }

     $info{from}

       Package the symbol comes from.

     $info{into}

       Package to which the symbol should be added.

     $info{sig}

       The sigil that should be used.

     $info{spec}

       Extra details.

     $info{symbol}

       The original symbol name (with sigil) from the original package.

   @SYMBOLS (optional)

     Symbols you wish to import. If no symbols are specified then the
     defaults will be used. You may also specify tags using the ':'
     prefix.

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

   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.

   my $exports = Importer->get($from, @imports)

     This returns hashref of { $name => $ref } for all the specified
     imports.

     $from should be the package from which to get the exports.

   my @export_refs = Importer->get_list($from, @imports)

     This returns a list of references for each import specified. Only the
     export references are returned, the names are not.

     $from should be the package from which to get the exports.

   $export_ref = Importer->get_one($from, $import)

     This returns a single reference to a single export. If you provide
     multiple imports then only the LAST one will be used.

     $from should be the package from which to get the exports.

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

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

   $imp = Importer->new(from => 'Some::Exporter', caller => [$package,
   $file, $line])

     This is how you create a new Importer instance. from =>
     'Some::Exporter' is the only required argument. You may also specify
     the caller => [...] arrayref, which will be used only for error
     reporting. If you do not specify a caller then Importer will attempt
     to find the caller dynamically every time it needs it (this is slow
     and expensive, but necessary if you intend to re-use the object.)

OBJECT METHODS

   $imp->do_import($into)

   $imp->do_import($into, @symbols)

     This will import from the objects from package into the $into
     package. You can provide a list of @symbols, or you can leave it
     empty for the defaults.

   $imp->do_unimport()

   $imp->do_unimport(@symbols)

     This will remove imported symbols from the objects from package. If
     you specify a list of @symbols then only the specified symbols will
     be removed, otherwise all symbols imported using Importer will be
     removed.

     Note: Please be aware of the difference between do_import() and
     do_unimport(). For import 'from' us used as the origin, in unimport
     it is used as the target. This means you cannot re-use an instance to
     import and then unimport.

   ($into, $versions, $exclude, $symbols, $set) =
   $imp->parse_args('Dest::Package')

   ($into, $versions, $exclude, $symbols, $set) =
   $imp->parse_args('Dest::Package', @symbols)

     This parses arguments. The first argument must be the destination
     package. Other arguments can be a mix of symbol names, tags,
     patterns, version numbers, and exclusions.

   $caller_ref = $imp->get_caller()

     This will find the caller. This is mainly used for error reporting.
     IF the object was constructed with a caller then that is what is
     returned, otherwise this will scan the stack looking for the first
     call that does not originate from a package that ISA Importer.

   $imp->carp($warning)

     Warn at the callers level.

   $imp->croak($exception)

     Die at the callers level.

   $from_package = $imp->from()

     Get the from package that was specified at construction.

   $file = $imp->from_file()

     Get the filename for the from package.

   $imp->load_from()

     This will load the from package if it has not been loaded already.
     This uses some magic to ensure errors in the load process are
     reported to the caller.

   $menu_hr = $imp->menu($into)

     Get the export menu built from, or provided by the from package. This
     is cached after the first time it is called. Use $imp->reload_menu()
     to refresh it.

     The menu structure looks like this:

         $menu = {
             # every valid export has a key in the lookup hashref, value is always
             # 1, key always includes the sigil
             lookup => {'&symbol_a' => 1, '$symbol_b' => 1, ...},

             # most exports are listed here, symbol name with sigil is key, value is
             # a reference to the symbol. If a symbol is missing it may be generated.
             exports => {'&symbol_a' => \&symbol_a, '$symbol_b' => \$symbol_b, ...},

             # Hashref of tags, tag name (without ':' prefix) is key, value is an
             # arrayref of symbol names, subs may have a sigil, but are not required
             # to.
             tags => { DEFAULT => [...], foo => [...], ... },

             # Magic to apply
             magic => { foo => sub { ... }, ... },

             # This is a hashref just like 'lookup'. Keys are symbols which may not
             # always be available. If there are no symbols in this category then
             # the value of the 'fail' key will be undef instead of a hashref.
             fail => { '&iffy_symbol' => 1, '\&only_on_linux' => 1 },
             # OR fail => undef,

             # If present, this subroutine knows how to generate references for the
             # symbols listed in 'lookup', but missing from 'exports'. References
             # this returns are NEVER cached.
             generate => sub { my $sym_name = shift; ...; return $symbol_ref },
         };

   $imp->reload_menu($into)

     This will reload the export menu from the from package.

   my $exports = $imp->get(@imports)

     This returns hashref of { $name => $ref } for all the specified
     imports.

   my @export_refs = $imp->get_list(@imports)

     This returns a list of references for each import specified. Only the
     export references are returned, the names are not.

   $export_ref = $imp->get_one($import)

     This returns a single reference to a single export. If you provide
     multiple imports then only the LAST one will be used.

FUNCTIONS

   These can be imported:

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

   $bool = optimal_import($from, $into, \@caller, @imports)

     This function will attempt to import @imports from the $from package
     into the $into package. @caller needs to have a package name,
     filename, and line number. If this function fails then no exporting
     will actually happen.

     If the import is successful this will return true.

     If the import is unsuccessful this will return false, and no
     modifications to the symbol table will occur.

   $class->import(@imports)

     If you write class intended to be used with Importer, but also need
     to provide a legacy import() method for direct consumers of your
     class, you can import this import() method.

         package My::Exporter;

         # This will give you 'import()' much like 'use base "Exporter";'
         use Importer 'Importer' => qw/import/;

         ...

SOURCE

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

MAINTAINERS

   Chad Granum <[email protected]>

AUTHORS

   Chad Granum <[email protected]>

COPYRIGHT

   Copyright 2015 Chad Granum <[email protected]>.

   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/

You are viewing proxied material from ftp.icm.edu.pl. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.