Exporter::Tiny::ManualUserpContributed PExporter::Tiny::Manual::Exporting(3pm)
NAME
Exporter::Tiny::Manual::Exporting - creating an exporter using
Exporter::Tiny
SYNOPSIS
Read Exporter::Tiny::Manual::QuickStart first!
DESCRIPTION
Simple configuration works the same as Exporter; inherit from
Exporter::Tiny, and use the @EXPORT, @EXPORT_OK, and %EXPORT_TAGS
package variables to list subs to export.
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.
Advanced Tag Stuff
You can define tags using other tags:
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.
More on 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 {
...;
}
}
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);
};
Hooks
Sometimes as well as exporting stuff, you want to do some setup or
something.
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.
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($globals)"
Documented above.
"_exporter_validate_unimport_opts($globals)"
Documented above.
"_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, $globals)"
Like "_exporter_expand_regexp", but given a regexp-like string
instead of a tag name.
The default implementation greps through @EXPORT_OK for imports,
and the list of already-imported functions for exports.
"_exporter_expand_sub($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 { $type->assert_return(@_) },
)
The default implementation checks that the name is allowed to be
exported (using the "_exporter_permitted_regexp" method), gets the
coderef using the generator if there is one (or by calling "can" on
your exporter otherwise) and calls "_exporter_fail" if it's unable
to generate or retrieve a coderef.
Despite the name, is also called for non-code symbols.
"_exporter_permitted_regexp($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, $coderef)"
This method actually installs the exported sub into its new
destination. Its return value is ignored.
The default implementation handles sub renaming (i.e. the "-as",
"-prefix" and "-suffix" functions. This method does a lot of stuff;
if you need to override it, it's probably a good idea to just pre-
process the arguments and then call the super method rather than
trying to handle all of it yourself.
Despite the name, is also called for non-code symbols.
"_exporter_uninstall_sub($name, $args, $globals)"
The opposite of "_exporter_install_sub".
SEE ALSO
Exporter::Shiny, Exporter::Tiny.
AUTHOR
Toby Inkster <tobyink@cpan.org>.
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.
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.
perl v5.36.0 2023-0Exporter::Tiny::Manual::Exporting(3pm)
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