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Manual Reference Pages  -  ROSE::OBJECT::MIXIN (3)

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Rose::Object::MixIn - A base class for mix-ins.



  package MyMixInClass;

  use Rose::Object::MixIn(); # Use empty parentheses here
  our @ISA = qw(Rose::Object::MixIn);

  __PACKAGE__->export_tag(all => [ qw(my_cool_method my_other_method) ]);

  sub my_cool_method  { ... }
  sub my_other_method { ... }

  package MyClass;
  # Import methods my_cool_method() and my_other_method()
  use MyMixInClass qw(:all);

  package MyOtherClass; 
  # Import just my_cool_method()
  use MyMixInClass qw(my_cool_method);

  package YetAnotherClass;
  # Import just my_cool_method() as cool()
  use MyMixInClass { my_cool_method => cool }


Rose::Object::MixIn is a base class for mix-ins. A mix-in is a class that exports methods into another class. This export process is controlled with an Exporter-like interface, but Rose::Object::MixIn does not inherit from Exporter.

When you use a Rose::Object::MixIn-derived class, its import method is called at compile time. In other words, this:

    use Rose::Object::MixIn a, b, { c => d };

is the same thing as this:

    BEGIN { Rose::Object::MixIn->import(a, b, { c => d }) }

To prevent the import method from being run, put empty parentheses () after the package name instead of a list of arguments.

    use Rose::Object::MixIn();

See the synopsis for an example of when this is handy: using Rose::Object::MixIn from within a subclass. Note that the empty parenthesis are important. The following is not equivalent:

    # This is not the same thing as the example above!
    use Rose::Object::MixIn;

See the documentation for the import method below to learn what arguments it accepts.


<B>import ARGSB> Import the methods specified by ARGS into the package from which this method was called. If the current class can already perform one of these methods, a fatal error will occur. To override an existing method, you must use the -force argument (see below).

Valid formats for ARGS are as follows:
o <B>A method nameB>

Literal method names will be imported as-is.

o <B>A tag nameB>

Tags names are indicated with a leading colon. For example, :all specifies the all tag. A tag is a stand-in for a list of methods. See the export_tag method to learn how to create tags.

o <B>A reference to a hashB>

Each key/value pair in this hash contains a method name and the name that it will be imported as. Use this feature to import methods under different names in order to avoid conflicts with existing methods.

o -force

The special literal argument -force will cause the specified methods to be imported even if the calling class can already perform one or more of those methods.

o -target_class CLASS

The special literal argument -target-class followed by a class name will cause the specified methods to be imported into CLASS rather than into the calling class.

See the synopsis for several examples of the import method in action. (Remember, it’s called implicitly when you use a Rose::Object::MixIn-derived class with anything other than an empty set of parenthesis () as an argument.)

<B>clear_export_tagsB> Delete the entire list of export tags.
<B>export_tag NAME [, ARRAYREF]B> Get or set the list of method names associated with a tag. The tag name should not begin with a colon. If ARRAYREF is passed, then the list of methods associated with the specific tag is set.

Returns a list (in list context) or a reference to an array (in scalar context) of method names. The array reference return value should be treated as read-only. If no such tag exists, and if an ARRAYREF is not passed, then a fatal error will occur.

<B>export_tagsB> Returns a list (in list context) and a reference to an array (in scalar context) containing the complete list of export tags. The array reference return value should be treated as read-only.


John C. Siracusa (


Copyright (c) 2010 by John C. Siracusa. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
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perl v5.20.3 ROSE::OBJECT::MIXIN (3) 2010-04-27

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