Unlike Exporter, 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 that your module (which is a subclass of Exporter::Tiny) can override them to provide interesting behaviour.
use Exporter::Shiny qw(
black white red green blue cyan magenta yellow
);
our %EXPORT_TAGS = (
rgb => [qw( red green blue )],
cym => [qw( cyan magenta yellow )],
cymk => [qw( black :cym )],
monochrome => [qw( black white )],
all => [qw( :rgb :cymk :monochrome )],
);
CAVEAT: If you create a cycle in the tags, this could put Exporter::Tiny into an infinite loop expanding the tags. Don't do that.
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 {
...;
}
}
We showed how to do that in Exporter::Tiny::Manual::QuickStart, but one thing we didn't show was that $globals gets passed in there. This is the global options hash, as described in Exporter::Tiny::Manual::Importing. It can often be useful. In particular it will tell you what package the generated sub is destined to be installed into.
To generate non-code symbols, name your generators like this:
sub _generateScalar_Foo { ... } # generate a symbol $Foo
sub _generateArray_Bar { ... } # generate a symbol @Bar
sub _generateHash_Baz { ... } # generate a symbol %Baz
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);
};
You can define a couple of class methods in your package, and they'll get called at the appropriate time:
package MyUtils;
...;
sub _exporter_validate_opts {
my $class = shift;
my ($globals) = @_;
...; # do stuff here
$class->SUPER::_exporter_validate_opts(@_);
}
sub _exporter_validate_unimport_opts {
my $class = shift;
my ($globals) = @_;
...; # do stuff here
$class->SUPER::_exporter_validate_unimport_opts(@_);
}
The $globals variable is that famous global options hash. In particular, "$globals->{into}" is useful because it tells you what package has imported you.
As you might have guessed, these methods were originally intended to validate the global options hash, but can be used to perform any general duties before the real exporting work is done.
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.)
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.
The default implementation greps through @EXPORT_OK for imports, and the list of already-imported functions for exports.
(
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.
Despite the name, is also called for non-code symbols.
The default implementation of this method assembles the regexp from @EXPORT and @EXPORT_OK.
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.
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.
Despite the name, is also called for non-code symbols.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.