NAME

       Import::Into - Import packages into other packages

SYNOPSIS

         package My::MultiExporter;

         use Import::Into;

         # simple
         sub import {
           Thing1->import::into(scalar caller);
         }

         # multiple
         sub import {
           my $target = caller;
           Thing1->import::into($target);
           Thing2->import::into($target, qw(import arguments));
         }

         # by level
         sub import {
           Thing1->import::into(1);
         }

         # with exporter
         use base qw(Exporter);
         sub import {
           shift->export_to_level(1);
           Thing1->import::into(1);
         }

         # no My::MultiExporter == no Thing1
         sub unimport {
           Thing1->unimport::out_of(scalar caller);
         }

       People wanting to re-export your module should also be using Import::Into.  Any exporter
       or pragma will work seamlessly.

       Note: You do not need to make any changes to Thing1 to be able to call "import::into" on
       it. This is a global method, and is callable on any package (and in fact on any object as
       well, although it's rarer that you'd want to do that).

DESCRIPTION

       Writing exporters is a pain. Some use Exporter, some use Sub::Exporter, some use
       Moose::Exporter, some use Exporter::Declare ... and some things are pragmas.

       Exporting on someone else's behalf is harder.  The exporters don't provide a consistent
       API for this, and pragmas need to have their import method called directly, since they
       effect the current unit of compilation.

       "Import::Into" provides global methods to make this painless.

METHODS

   $package->import::into( $target, @arguments );
       A global method, callable on any package.  Loads and imports the given package into
       $target.  @arguments are passed along to the package's import method.

       $target can be an package name to export to, an integer for the caller level to export to,
       or a hashref with the following options:

       package
           The target package to export to.

       filename
           The apparent filename to export to.  Some exporting modules, such as autodie or
           strictures, care about the filename they are being imported to.

       line
           The apparent line number to export to.  To be combined with the "filename" option.

       level
           The caller level to export to.  This will automatically populate the "package",
           "filename", and "line" options, making it the easiest most constent option.

       version
           A version number to check for the module.  The equivalent of specifying the version
           number on a "use" line.

   $package->unimport::out_of( $target, @arguments );
       Equivalent to "import::into", but dispatches to $package's "unimport" method instead of
       "import".

WHY USE THIS MODULE

       The APIs for exporting modules aren't consistent.  Exporter subclasses provide
       export_to_level, but if they overrode their import method all bets are off.  Sub::Exporter
       provides an into parameter but figuring out something used it isn't trivial. Pragmas need
       to have their "import" method called directly since they affect the current unit of
       compilation.

       It's ... annoying.

       However, there is an approach that actually works for all of these types.

         eval "package $target; use $thing;"

       will work for anything checking caller, which is everything except pragmas.  But it
       doesn't work for pragmas - pragmas need:

         $thing->import;

       because they're designed to affect the code currently being compiled - so within an eval,
       that's the scope of the eval itself, not the module that just "use"d you - so

         sub import {
           eval "use strict;"
         }

       doesn't do what you wanted, but

         sub import {
           strict->import;
         }

       will apply strict to the calling file correctly.

       Of course, now you have two new problems - first, that you still need to know if
       something's a pragma, and second that you can't use either of these approaches alone on
       something like Moose or Moo that's both an exporter and a pragma.

       So, a solution for that is:

         use Module::Runtime;
         my $sub = eval "package $target; sub { use_module(shift)->import(\@_) }";
         $sub->($thing, @import_args);

       which means that import is called from the right place for pragmas to take effect, and
       from the right package for caller checking to work - and so behaves correctly for all
       types of exporter, for pragmas, and for hybrids.

       Additionally, some import routines check the filename they are being imported to.  This
       can be dealt with by generating a #line directive in the eval, which will change what
       "caller" reports for the filename when called in the importer. The filename and line
       number to use in the directive then need to be fetched using "caller":

         my ($target, $file, $line) = caller(1);
         my $sub = eval qq{
           package $target;
         #line $line "$file"
           sub { use_module(shift)->import(\@_) }
         };
         $sub->($thing, @import_args);

       And you need to switch between these implementations depending on if you are targeting a
       specific package, or something in your call stack.

       Remembering all this, however, is excessively irritating. So I wrote a module so I didn't
       have to anymore. Loading Import::Into creates a global method "import::into" which you can
       call on any package to import it into another package. So now you can simply write:

         use Import::Into;

         $thing->import::into($target, @import_args);

       This works because of how perl resolves method calls - a call to a simple method name is
       resolved against the package of the class or object, so

         $thing->method_name(@args);

       is roughly equivalent to:

         my $code_ref = $thing->can('method_name');
         $code_ref->($thing, @args);

       while if a "::" is found, the lookup is made relative to the package name (i.e. everything
       before the last "::") so

         $thing->Package::Name::method_name(@args);

       is roughly equivalent to:

         my $code_ref = Package::Name->can('method_name');
         $code_ref->($thing, @args);

       So since Import::Into defines a method "into" in package "import" the syntax reliably
       calls that.

       For more craziness of this order, have a look at the article I wrote at
       <http://shadow.cat/blog/matt-s-trout/madness-with-methods> which covers coderef abuse and
       the "${\...}" syntax.

       And that's it.

SEE ALSO

       I gave a lightning talk on this module (and curry and Safe::Isa) at YAPC::NA 2013
       <https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>.

ACKNOWLEDGEMENTS

       Thanks to Getty for asking "how can I get "use strict; use warnings;" turned on for all
       consumers of my code?" and then "why is this not a module?!".

AUTHOR

       mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>

CONTRIBUTORS

       haarg - Graham Knop (cpan:HAARG) <haarg@haarg.org>

       Mithaldu - Christian Walde (cpan:MITHALDU) <walde.christian@gmail.com>

COPYRIGHT

       Copyright (c) 2012 the Import::Into "AUTHOR" and "CONTRIBUTORS" as listed above.

LICENSE

       This library is free software and may be distributed under the same terms as perl itself.