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.\" ========================================================================
.\"
.IX Title "Rose::Object::MixIn 3pm"
.TH Rose::Object::MixIn 3pm "2021-01-03" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
Rose::Object::MixIn \- A base class for mix\-ins.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  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 => \*(Aqcool\*(Aq }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
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.
.PP
When you use a Rose::Object::MixIn\-derived class, its import method is called at compile time.  In other words, this:
.PP
.Vb 1
\&    use Rose::Object::MixIn \*(Aqa\*(Aq, \*(Aqb\*(Aq, { c => \*(Aqd\*(Aq };
.Ve
.PP
is the same thing as this:
.PP
.Vb 1
\&    BEGIN { Rose::Object::MixIn\->import(\*(Aqa\*(Aq, \*(Aqb\*(Aq, { c => \*(Aqd\*(Aq }) }
.Ve
.PP
To prevent the import method from being run, put empty parentheses \*(L"()\*(R" after the package name instead of a list of arguments.
.PP
.Vb 1
\&    use Rose::Object::MixIn();
.Ve
.PP
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 \fInot\fR equivalent:
.PP
.Vb 2
\&    # This is not the same thing as the example above!
\&    use Rose::Object::MixIn;
.Ve
.PP
See the documentation for the import method below to learn what arguments it accepts.
.SH "CLASS METHODS"
.IX Header "CLASS METHODS"
.IP "\fBimport \s-1ARGS\s0\fR" 4
.IX Item "import ARGS"
Import the methods specified by \s-1ARGS\s0 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 \f(CW\*(C`\-force\*(C'\fR argument (see below).
.Sp
Valid formats for \s-1ARGS\s0 are as follows:
.RS 4
.IP "\(bu" 4
\&\fBA method name\fR
.Sp
Literal method names will be imported as-is.
.IP "\(bu" 4
\&\fBA tag name\fR
.Sp
Tags names are indicated with a leading colon.  For example, \*(L":all\*(R" specifies the \*(L"all\*(R" tag.  A tag is a stand-in for a list of methods.  See the export_tag method to learn how to create tags.
.IP "\(bu" 4
\&\fBA reference to a hash\fR
.Sp
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.
.IP "\(bu" 4
\&\f(CW\*(C`\-force\*(C'\fR
.Sp
The special literal argument \f(CW\*(C`\-force\*(C'\fR will cause the specified methods to be imported even if the calling class can already perform one or more of those methods.
.IP "\(bu" 4
\&\f(CW\*(C`\-target_class CLASS\*(C'\fR
.Sp
The special literal argument \f(CW\*(C`\-target\-class\*(C'\fR followed by a class name will cause the specified methods to be imported into \s-1CLASS\s0 rather than into the calling class.
.RE
.RS 4
.Sp
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 \*(L"()\*(R" as an argument.)
.RE
.IP "\fBclear_export_tags\fR" 4
.IX Item "clear_export_tags"
Delete the entire list of export tags.
.IP "\fBexport_tag \s-1NAME\s0 [, \s-1ARRAYREF\s0]\fR" 4
.IX Item "export_tag NAME [, ARRAYREF]"
Get or set the list of method names associated with a tag.  The tag name should \fInot\fR begin with a colon.  If \s-1ARRAYREF\s0 is passed, then the list of methods associated with the specific tag is set.
.Sp
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 \s-1ARRAYREF\s0 is not passed, then a fatal error will occur.
.IP "\fBexport_tags\fR" 4
.IX Item "export_tags"
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.
.SH "AUTHOR"
.IX Header "AUTHOR"
John C. Siracusa (siracusa@gmail.com)
.SH "LICENSE"
.IX Header "LICENSE"
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.