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Toby Inkster

NAME

Exporter::Tiny - an exporter with the features of Sub::Exporter but only core dependencies

SYNOPSIS

   package MyUtils;
   use base "Exporter::Tiny";
   our @EXPORT = qw(frobnicate);
   sub frobnicate { my $n = shift; ... }
   1;

   package MyScript;
   use MyUtils "frobnicate" => { -as => "frob" };
   print frob(42);
   exit;

DESCRIPTION

Exporter::Tiny supports many of Sub::Exporter's external-facing features including renaming imported functions with the -as, -prefix and -suffix options; explicit destinations with the into option; and alternative installers with the installler option. But it's written in only about 40% as many lines of code and with zero non-core dependencies.

Its internal-facing interface is closer to Exporter.pm, with configuration done through the @EXPORT, @EXPORT_OK and %EXPORT_TAGS package variables.

Exporter::Tiny performs most of its internal duties (including resolution of tag names to sub names, resolution of sub names to coderefs, and installation of coderefs into the target package) as method calls, which means they can be overridden to provide interesting behaviour.

Utility Functions

These are really for internal use, but can be exported if you need them.

mkopt(\@array)

Similar to mkopt from Data::OptList. It doesn't support all the fancy options that Data::OptList does (moniker, require_unique, must_be and name_test) but runs about 50% faster.

mkopt_hash(\@array)

Similar to mkopt_hash from Data::OptList. See also mkopt.

TIPS AND TRICKS IMPORTING FROM EXPORTER::TINY

For the purposes of this discussion we'll assume we have a module called MyUtils which exports one function, frobnicate. MyUtils inherits from Exporter::Tiny.

Many of these tricks may seem familiar from Sub::Exporter. That is intentional. Exporter::Tiny doesn't attempt to provide every feature of Sub::Exporter, but where it does it usually uses a fairly similar API.

Basic importing

   # import "frobnicate" function
   use MyUtils "frobnicate";

   # import all functions that MyUtils offers
   use MyUtils -all;

Renaming imported functions

   # call it "frob"
   use MyUtils "frobnicate" => { -as => "frob" };

   # call it "my_frobnicate"
   use MyUtils "frobnicate" => { -prefix => "my_" };

   # call it "frobnicate_util"
   use MyUtils "frobnicate" => { -suffix => "_util" };

   # import it twice with two different names
   use MyUtils
      "frobnicate" => { -as => "frob" },
      "frobnicate" => { -as => "frbnct" };

Lexical subs

   {
      use Sub::Exporter::Lexical lexical_installer => { -as => "lex" };
      use MyUtils { installer => lex }, "frobnicate";
      
      frobnicate(...);  # ok
   }
   
   frobnicate(...);  # not ok

Import functions into another package

   use MyUtils { into => "OtherPkg" }, "frobnicate";
   
   OtherPkg::frobincate(...);

Import functions into a scalar

   my $func;
   use MyUtils "frobnicate" => { -as => \$func };
   
   $func->(...);

Import functions into a hash

OK, Sub::Exporter doesn't do this...

   my %funcs;
   use MyUtils { into => \%funcs }, "frobnicate";
   
   $funcs{frobnicate}->(...);

DO NOT WANT!

This imports everything except "frobnicate":

   use MyUtils qw( -all !frobnicate );

Negated imports always "win", so the following will not import "frobnicate", no matter how many times you repeat it...

   use MyUtils qw( !frobnicate frobnicate frobnicate frobnicate );

Importing by regexp

Here's how you could import all functions beginning with an "f":

   use MyUtils qw( /^F/i );

Or import everything except functions beginning with a "z":

   use MyUtils qw( -all !/^Z/i );

Note that regexps are always supplied as strings starting with "/", and not as quoted regexp references (qr/.../).

TIPS AND TRICKS EXPORTING USING EXPORTER::TINY

Simple configuration works the same as Exporter; inherit from this module, and use the @EXPORT, @EXPORT_OK and %EXPORT_TAGS package variables to list subs to export.

Generators

Exporter::Tiny has always allowed exported subs to be generated (like Sub::Exporter), but until version 0.025 did not have an especially nice API for it.

Now, it's easy. If you want to generate a sub foo to export, list it in @EXPORT or @EXPORT_OK as usual, and then simply give your exporter module a class method called _generate_foo.

   push @EXPORT_OK, 'foo';
   
   sub _generate_foo {
      my $class = shift;
      my ($name, $args, $globals) = @_;
      
      return sub {
         ...;
      }
   }

You can also generate tags:

   my %constants;
   BEGIN {
      %constants = (FOO => 1, BAR => 2);
   }
   use constant \%constants;
   
   $EXPORT_TAGS{constants} = sub {
      my $class = shift;
      my ($name, $args, $globals) = @_;
      
      return keys(%constants);
   };

Overriding Internals

An important difference between Exporter and Exporter::Tiny is that the latter calls all its internal functions as class methods. This means that your subclass can override them to alter their behaviour.

The following methods are available to be overridden. Despite being named with a leading underscore, they are considered public methods. (The underscore is there to avoid accidentally colliding with any of your own function names.)

_exporter_validate_opts($globals)

This method is called once each time import is called. It is passed a reference to the global options hash. (That is, the optional leading hashref in the use statement, where the into and installer options can be provided.)

You may use this method to munge the global options, or validate them, throwing an exception or printing a warning.

The default implementation does nothing interesting.

_exporter_merge_opts($tag_opts, $globals, @exports)

Called to merge options which have been provided for a tag into the options provided for the exports that the tag expanded to.

_exporter_expand_tag($name, $args, $globals)

This method is called to expand an import tag (e.g. ":constants"). It is passed the tag name (minus the leading ":"), an optional hashref of options (like { -prefix => "foo_" }), and the global options hashref.

It is expected to return a list of ($name, $args) arrayref pairs. These names can be sub names to export, or further tag names (which must have their ":"). If returning tag names, be careful to avoid creating a tag expansion loop!

The default implementation uses %EXPORT_TAGS to expand tags, and provides fallbacks for the :default and :all tags.

_exporter_expand_regexp($regexp, $args, $globals)

Like _exporter_expand_regexp, but given a regexp-like string instead of a tag name.

The default implementation greps through @EXPORT_OK.

_exporter_expand_sub($name, $args, $globals)

This method is called to translate a sub name to a hash of name => coderef pairs for exporting to the caller. In general, this would just be a hash with one key and one value, but, for example, Type::Library overrides this method so that "+Foo" gets expanded to:

   (
      Foo         => sub { $type },
      is_Foo      => sub { $type->check(@_) },
      to_Foo      => sub { $type->assert_coerce(@_) },
      assert_Foo  => sub { $type->assert_return(@_) },
   )

The default implementation checks that the name is allowed to be exported (using the _exporter_permitted_regexp method), gets the coderef using the generator if there is one (or by calling can on your exporter otherwise) and calls _exporter_fail if it's unable to generate or retrieve a coderef.

_exporter_permitted_regexp($globals)

This method is called to retrieve a regexp for validating the names of exportable subs. If a sub doesn't match the regexp, then the default implementation of _exporter_expand_sub will refuse to export it. (Of course, you may override the default _exporter_expand_sub.)

The default implementation of this method assembles the regexp from @EXPORT and @EXPORT_OK.

_exporter_fail($name, $args, $globals)

Called by _exporter_expand_sub if it can't find a coderef to export.

The default implementation just throws an exception. But you could emit a warning instead, or just ignore the failed export.

If you don't throw an exception then you should be aware that this method is called in list context, and any list it returns will be treated as an _exporter_expand_sub-style hash of names and coderefs for export.

_exporter_install_sub($name, $args, $globals, $coderef)

This method actually installs the exported sub into its new destination. Its return value is ignored.

The default implementation handles sub renaming (i.e. the -as, -prefix and -suffix functions. This method does a lot of stuff; if you need to override it, it's probably a good idea to just pre-process the arguments and then call the super method rather than trying to handle all of it yourself.

HISTORY

Type::Library had a bunch of custom exporting code which poked coderefs into its caller's stash. It needed this to be something more powerful than most exporters so that it could switch between exporting Moose, Mouse and Moo-compatible objects on request. Sub::Exporter would have been capable, but had too many dependencies for the Type::Tiny project.

Meanwhile Type::Utils, Types::TypeTiny and Test::TypeTiny each used the venerable Exporter.pm. However, this meant they were unable to use the features like Sub::Exporter-style function renaming which I'd built into Type::Library:

   ## import "Str" but rename it to "String".
   use Types::Standard "Str" => { -as => "String" };

And so I decided to factor out code that could be shared by all Type-Tiny's exporters into a single place: Exporter::TypeTiny.

As of version 0.026, Exporter::TypeTiny was also made available as Exporter::Tiny, distributed independently on CPAN. CHOCOLATEBOY had convinced me that it was mature enough to live a life of its own.

As of version 0.030, Type-Tiny depends on Exporter::Tiny and Exporter::TypeTiny is being phased out.

OBLIGATORY EXPORTER COMPARISON

Exporting is unlikely to be your application's performance bottleneck, but nonetheless here are some comparisons.

Comparative sizes according to Devel::SizeMe:

   Exporter                     217.1Kb
   Sub::Exporter::Progressive   263.2Kb
   Exporter::Tiny               267.7Kb
   Exporter + Exporter::Heavy   281.5Kb
   Exporter::Renaming           406.2Kb
   Sub::Exporter                701.0Kb

Performance exporting a single sub:

              Rate     SubExp    ExpTiny SubExpProg      ExpPM
SubExp      2489/s         --       -56%       -85%       -88%
ExpTiny     5635/s       126%         --       -67%       -72%
SubExpProg 16905/s       579%       200%         --       -16%
ExpPM      20097/s       707%       257%        19%         --

(Exporter::Renaming globally changes the behaviour of Exporter.pm, so could not be included in the same benchmarks.)

(Non-Core) Dependencies:

   Exporter                    -1
   Exporter::Renaming           0
   Exporter::Tiny               0
   Sub::Exporter::Progressive   0
   Sub::Exporter                3

Features:

                                      ExpPM   ExpTiny SubExp  SubExpProg
 Can export code symbols............. Yes     Yes     Yes     Yes      
 Can export non-code symbols......... Yes                              
 Groups/tags......................... Yes     Yes     Yes     Yes      
 Config avoids package variables.....                 Yes              
 Allows renaming of subs.............         Yes     Yes     Maybe    
 Install code into scalar refs.......         Yes     Yes     Maybe    
 Can be passed an "into" parameter...         Yes     Yes     Maybe    
 Can be passed an "installer" sub....         Yes     Yes     Maybe    
 Supports generators.................         Yes     Yes              
 Sane API for generators.............         Yes     Yes              

(Certain Sub::Exporter::Progressive features are only available if Sub::Exporter is installed.)

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Exporter-Tiny.

SUPPORT

IRC: support is available through in the #moops channel on irc.perl.org.

SEE ALSO

Exporter::Shiny, Sub::Exporter, Exporter.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2013-2014 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.




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