=pod

=encoding utf-8

=for stopwords frobnicate greps regexps

=head1 NAME

Exporter::Tiny::Manual::Importing - importing from Exporter::Tiny-based modules

=head1 DESCRIPTION

For the purposes of this discussion we'll assume we have a module called
C<< MyUtils >> which exports functions called C<frobnicate>, C<red>,
C<blue>, and C<green>. It has a tag set up called C<:colours> which
corresponds to C<red>, C<blue>, and C<green>.

Many of these tricks may seem familiar from L<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.

=head2 Basic importing

It's easy to import a single function from a module:

   use MyUtils "frobnicate";

Or a list of functions:

   use MyUtils "red", "green";

Perl's C<< qw() >> shorthand for a list of words is pretty useful:

   use MyUtils qw( red green );

If the module defines tags, you can import them like this:

   use MyUtils qw( :colours );

Or with a hyphen instead of a colon:

   use MyUtils qw( -colours );

Hyphens are good because Perl will autoquote a bareword that follows
them:

   use MyUtils -colours;

And it's possible to mix function names and tags in the same list:

   use MyUtils qw( frobnicate :colours );

=head2 Renaming imported functions

It's possible to rename a function you're importing:

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

Or you can apply a prefix and/or suffix. The following imports the
function and calls it C<my_frobinate_thing>.

   use MyUtils "frobnicate" => { -prefix => "my_", -suffix => "_thing" };

You can apply a prefix/suffix to B<all> functions you import by
placing the hashref B<first> in the import list. (This first hashref
is referred to as the global options hash, and can do some special
things.)

   use MyUtils { prefix => "my_" }, "frobnicate";

Did you notice that we used C<< -prefix >> and C<< -suffix >> in the
normal options hash, but C<< prefix >> and C<< suffix >> (no hyphen)
in the global options hash? That's a common pattern with this module.

You can import the same function multiple times with different names:

   use MyUtils
      "frobnicate" => { -as => "frob" },
      "frobnicate" => { -as => "frbnct" };

Tags can take the C<< -prefix >> and C<< -suffix >> options too. The 
following imports C<colour_red>, C<colour_green>, and C<colour_blue>:

   use MyUtils -colours => { -prefix => "colour_" };

You can also set C<< -as >> to be a coderef to generate a function
name. This imports functions called C<RED>, C<GREEN>, and C<BLUE>:

   use MyUtils -colours => { -as => sub { uc($_[0]) } };

Note that it doesn't make sense to use C<< -as >> with a tag unless
you're doing this coderef thing. Coderef C<< as >> also works in the
global options hash.

=head2 DO NOT WANT!

Sometimes you want to supply a list of functions you B<< don't >> want
to import. To do that, prefix the function with a bang. This imports
everything except "frobnicate":

   use MyUtils qw( -all !frobnicate );

You can add the bang prefix to tags too. This will import everything
except the colours.

   use MyUtils qw( -all !:colours );

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 );

=head2 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 I<strings> starting with
C<< "/" >>, and not as quoted regexp references (C<< qr/.../ >>).

=head2 Import functions into another package

Occasionally you need to import functions not into your own package,
but into a different package. You can do that like this:

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

However, L<Import::Into> will probably provide you with a better
approach which doesn't just work with Exporter::Tiny, but B<all>
exporters.

=head2 Lexical subs

Often you want to make use of an exported function, but don't want
it to "pollute" your namespace.

There is this L<Sub::Exporter::Lexical> thing that was designed as a
plugin for L<Sub::Exporter>, but Exporter::Tiny's API is close enough
that it will work. Do you remember that global options hash? Just
use that to tell Exporter::Tiny to use an alternative sub installer.

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

Another way to do lexical functions is to import a function into a
scalar variable:

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

You can even provide a hashref to put all imported functions into as
part of that global options hash I mentioned earlier.

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

=head2 Unimporting

You can unimport the functions that MyUtils added to your namespace:

   no MyUtils;

Or just specific ones:

   no MyUtils qw(frobnicate);

If you renamed a function when you imported it, you should unimport by
the new name:

   use MyUtils frobnicate => { -as => "frob" };
   ...;
   no MyUtils "frob";

Unimporting using tags and regexps should mostly do what you want.

=head1 DIAGNOSTICS

=over

=item B<< Overwriting existing sub '%s::%s' with sub '%s' exported by %s >>

A warning issued if Exporter::Tiny is asked to export a symbol which
will result in an existing sub being overwritten. This warning can be
suppressed using either of the following:

   use MyUtils { replace => 1 }, "frobnicate";
   use MyUtils "frobnicate" => { -replace => 1 };

Or can be upgraded to a fatal error:

   use MyUtils { replace => "die" }, "frobnicate";
   use MyUtils "frobnicate" => { -replace => "die" };

=item B<< Refusing to overwrite existing sub '%s::%s' with sub '%s' exported by %s >>

The fatal version of the above warning.

=item B<< Could not find sub '%s' exported by %s >>

You requested to import a sub which the package does not provide.

=item B<< Cannot provide an -as option for tags >>

Because a tag may provide more than one function, it does not make sense
to request a single name for it. Instead use C<< -prefix >> or C<< -suffix >>.

=item B<< Passing options to unimport '%s' makes no sense >>

When you import a sub, it occasionally makes sense to pass some options
for it. However, when unimporting, options do nothing, so this warning
is issued.

=back

=head1 SEE ALSO

L<Exporter::Shiny>,
L<Exporter::Tiny>.

=head1 AUTHOR

Toby Inkster E<lt>tobyink@cpan.orgE<gt>.

=head1 COPYRIGHT AND LICENCE

This software is copyright (c) 2013-2014, 2017 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.

=head1 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.