Declarative function exporting
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    Exporter::Declare - Exporting done right

    Exporter::Declare is a meta-driven exporting tool. Exporter::Declare
    tries to adopt all the good features of other exporting tools, while
    throwing away horrible interfaces. Exporter::Declare also provides hooks
    that allow you to add options and arguments for import. Finally,
    Exporter::Declare's meta-driven system allows for top-notch

    Declarative exporting (like Moose for exporting)
    Meta-driven for introspection
    Customizable import() method
    Export groups (tags)
    Export generators for subs and variables
    Clear and concise OO API
    Exports are blessed, allowing for more introspection
    Import syntax based off of Sub::Exporter
    Packages export aliases

        package Some::Exporter;
        use Exporter::Declare;

        default_exports qw/ do_the_thing /;
        exports qw/ subA subB $SCALAR @ARRAY %HASH /;

        # Create a couple tags (import lists)
        export_tag subs => qw/ subA subB do_the_thing /;
        export_tag vars => qw/ $SCALAR @ARRAY %HASH /;

        # These are simple boolean options, pass '-optionA' to enable it.
        import_options   qw/ optionA optionB /;

        # These are options which slurp in the next argument as their value, pass
        # '-optionC' => 'foo' to give it a value.
        import_arguments qw/ optionC optionD /;

        export anon_export => sub { ... };
        export '@anon_var' => [...];

        default_export a_default => sub { 'default!' }

        our $X = "x";
        default_export '$X';

        my $iterator = 'a';
        gen_export unique_class_id => sub {
            my $current = $iterator++;
            return sub { $current };

        gen_default_export '$my_letter' => sub {
            my $letter = $iterator++;
            return \$letter;

        # You can create a function to mangle the arguments before they are
        # parsed into a Exporter::Declare::Spec object.
        sub alter_import_args {
           my ($class, $args) = @_;

           # fiddle with args before importing routines are called
           @$args = grep { !/^skip_/ } @$args

        # There is no need to fiddle with import() or do any wrapping.
        # the $specs data structure means you generally do not need to parse
        # arguments yourself (but you can if you want using alter_import_args())

        # Change the spec object before export occurs
        sub before_import {
            my $class = shift;
            my ( $importer, $specs ) = @_;

            if ($specs->config->{optionA}) {
                # Modify $spec attributes accordingly

        # Use spec object after export occurs
        sub after_import {
            my $class = shift;
            my ( $importer, $specs ) = @_;

            do_option_a() if $specs->config->{optionA};

            do_option_c( $specs->config->{optionC} )
                if $specs->config->{optionC};

            print "-subs tag was used\n"
                if $specs->config->{subs};

            print "exported 'subA'\n"
                if $specs->exports->{subA};


        package Some::Importer;
        use Some::Exporter qw/ subA $SCALAR !%HASH /,
                            -default => { -prefix => 'my_' },
                            qw/ -optionA !-optionB /,
                            subB => { -as => 'sub_b' };

        print $SCALAR;


    Importing from a package that uses Exporter::Declare will be familiar to
    anyone who has imported from modules before. Arguments are all assumed
    to be export names, unless prefixed with "-" or ":" In which case they
    may be a tag or an option. Exports without a sigil are assumed to be
    code exports, variable exports must be listed with their sigil.

    Items prefixed with the "!" symbol are forcfully excluded, regardless of
    any listed item that may normally include them. Tags can also be
    excluded, this will effectively exclude everything in the tag.

    Tags are simply lists of exports, the exporting class may define any
    number of tags. Exporter::Declare also has the concept of options, they
    have the same syntax as tags. Options may be boolean or argument based.
    Boolean options are actually 3 value, undef, false "!", or true.
    Argument based options will grab the next value in the arguments list as
    their own, regardless of what type of value it is.

    When you use the module, or call import(), all the arguments are
    transformed into an Exporter::Declare::Specs object. Arguments are
    parsed for you into a list of imports, and a configuration hash in which
    tags/options are keys. Tags are listed in the config hash as true,
    false, or undef depending on if they were included, negated, or
    unlisted. Boolean options will be treated in the same way as tags.
    Options that take arguments will have the argument as their value.

    Exports can be subs, or package variables (scalar, hash, array). For
    subs simply ask for the sub by name, you may optionally prefix the subs
    name with the sub sigil "&". For variables list the variable name along
    with its sigil "$, %, or @".

        use Some::Exporter qw/ somesub $somescalar %somehash @somearray /;

    Every exporter automatically has the following 3 tags, in addition they
    may define any number of custom tags. Tags can be specified by their
    name prefixed by either "-" or ":".

        This tag may be used to import everything the exporter provides.

        This tag is used to import the default items exported. This will be
        used when no argument is provided to import.

        Every package has an alias that it can export. This is the last
        segmant of the packages namespace. IE "My::Long::Package::Name::Foo"
        could export the "Foo()" function. These alias functionis simply
        return the full package name as a string, in this case
        'My::Long::Package::Name::Foo'. This is similar to aliased.

        The -alias tag is a shortcut so that you do not need to think about
        what the alias name would be when adding it to the import arguments.

            use My::Long::Package::Name::Foo -alias;

            my $foo = Foo()->new(...);

    You can prefix, suffix, or completely rename the items you import.
    Whenever an item is followed by a hash in the import list, that hash
    will be used for configuration. Configuration items always start with a
    dash "-".

    The 3 available configuration options that effect import names are
    "-prefix", "-suffix", and "-as". If "-as" is seen it will be used as is.
    If prefix or suffix are seen they will be attached to the original name
    (unless -as is present in which case they are ignored).

        use Some::Exporter subA => { -as => 'DoThing' },
                           subB => { -prefix => 'my_', -suffix => '_ok' };

    The example above will import "subA()" under the name "DoThing()". It
    will also import "subB()" under the name "my_subB_ok()".

    You may als specify a prefix and/or suffix for tags. The following
    example will import all the default exports with 'my_' prefixed to each

        use Some::Exporter -default => { -prefix => 'my_' };

    Some exporters will recognise options. Options look just like tags, and
    are specified the same way. What options do, and how they effect things
    is exporter-dependant.

        use Some::Exporter qw/ -optionA -optionB /;

    Some options require an argument. These options are just like other
    tags/options except that the next item in the argument list is slurped
    in as the option value.

        use Some::Exporter -ArgOption    => 'Value, not an export',
                           -ArgTakesHash => { ... };

    Once again available options are exporter specific.

    Some items are generated at import time. These items may accept
    arguments. There are 3 ways to provide arguments, and they may all be
    mixed (though that is not recommended).

    As a hash

        use Some::Exporter generated => { key => 'val', ... };

    As an array

        use Some::Exporter generated => [ 'Arg1', 'Arg2', ... ];

    As an array in a config hash

        use Some::Exporter generated => { -as => 'my_gen', -args => [ 'arg1', ... ]};

    You can use all three at once, but this is really a bad idea, documented
    for completeness:

        use Some::Exporter generated => { -as => 'my_gen, key => 'value', -args => [ 'arg1', 'arg2' ]}
                           generated => [ 'arg3', 'arg4' ];

    The example above will work fine, all the arguments will make it into
    the generator. The only valid reason for this to work is that you may
    provide arguments such as "-prefix" to a tag that brings in generator(),
    while also desiring to give arguments to generator() independantly.

    With the exception of import(), all the following work equally well as
    functions or class methods.

    import( @args )
        The import() class method. This turns the @args list into an
        Exporter::Declare::Specs object.

    exports( @add_items )
        Add items to be exported.

    @list = exports()
        Retrieve list of exports.

    default_exports( @add_items )
        Add items to be exported, and add them to the -default tag.

    @list = default_exports()
        List of exports in the -default tag

        Specify boolean options that should be accepted at import time.

        Specify options that should be accepted at import that take

    export_tag( $name, @add_items );
        Define an export tag, or add items to an existing tag.

    These all work fine in function or method form, however the syntax sugar
    will only work in function form.

    reexport( $package )
        Make this exporter inherit all the exports and tags of $package.
        Works for Exporter::Declare or based exporters.
        Re-Exporting of Sub::Exporter based classes is not currently

    export_to( $package, @args )
        Export to the specified class.

    export( $name )
    export( $name, $ref )
        export is a keyword that lets you export any 1 item at a time. The
        item can be exported by name, or name + ref. When a ref is provided,
        the export is created, but there is no corresponding variable/sub in
        the packages namespace.

    default_export( $name )
    default_export( $name, $ref )
    gen_export( $name )
    gen_export( $name, $ref )
    gen_default_export( $name )
    gen_default_export( $name, $ref )
        These all act just like export(), except that they add subrefs as
        generators, and/or add exports to the -default tag.

    Please use Exporter::Declare::Magic directly from now on.

        use Exporter::Declare '-magic';

    This adds Devel::Declare magic to several functions. It also allows you
    to easily create or use parsers on your own exports. See
    Exporter::Declare::Magic for more details.

    You can also provide import arguments to Devel::Declare::Magic

        # Arguments to -magic must be in an arrayref, not a hashref.
        use Exporter::Declare -magic => [ '-default', '!export', -prefix => 'magic_' ];

    Exporter/ does not have much logic to speak of. Rather
    Exporter::Declare is sugar on top of class meta data stored in
    Exporter::Declare::Meta objects. Arguments are parsed via
    Exporter::Declare::Specs, and also turned into objects. Even exports are
    blessed references to the exported item itself, and handle the injection
    on their own (See Exporter::Declare::Export).

    All exporters have a meta class, the only way to get the meta object is
    to call the exporter_meta() method on the class/object that is an
    exporter. Any class that uses Exporter::Declare gets this method, and a

    Chad Granum

    Copyright (C) 2010 Chad Granum

    Exporter-Declare is free software; Standard perl licence.

    Exporter-Declare is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    more details.