Data::Grove






Data::Grove −− support for deeply nested structures


 use Data::Grove;

      $object = MyPackage‐>new;

      package MyPackage;
 @ISA = qw{Data::Grove};

"Data::Grove" provides support for deeply nested tree or
graph structures.  "Data::Grove" is intended primarily for
Perl module authors writing modules with many types or
classes of objects that need to be manipulated and extended
in a consistent and flexible way.

     "Data::Grove" is best used by creating a core set of
‘‘data’’ classes and then incrementally adding functionality
to the core data classes by using ‘‘extension’’ modules.
One reason for this design is so that the data classes can
be swapped out and the extension modules can work with new
data sources.  For example, these other data sources could
be disk−based, network‐based or built on top of a relational
database.

     Two extension modules that come with "Data::Grove" are
"Data::Grove::Parent" and "Data::Grove::Visitor".
"Data::Grove::Parent" adds a ‘"Parent"’ property to grove
objects and implements a ‘"root"’ method to grove objects to
return the root node of the tree from anywhere in the tree
and a ‘"rootpath"’ method to return a list of nodes between
the root node and ‘‘this’’ node.  "Data::Grove::Visitor"
adds callback methods ‘"accept"’ and ‘"accept_name"’ that
call your handler or receiver module back by object type
name or the object’s name.

     "Data::Grove" objects do not contain parent references,
Perl garbage collection will delete them when no longer
referenced and sub‐structures can be shared among several
structures.  "Data::Grove::Parent" is used to create
temporary objects with parent pointers.

     Properties of data classes are accessed directly using
Perl’s hash functions (i.e. ‘"$object−>{Property}"’).
Extension modules may also define properties that they
support or use, for example Data::Grove::Parent adds
‘"Parent"’ and ‘"Raw"’ properties and Visitor depends on
‘"Name"’ and ‘"Content"’ properties.

     See the module "XML::Grove" for an example
implementation of "Data::Grove".












                             ‐2‐




new( PROPERTIES )
    Return a new object blessed into the SubClass, with the
    given properties.  PROPERTIES may either be a list of
    key/value pairs, a single hash containing key/value
    pairs, or an existing "Data::Grove" object.  If an
    existing "Data::Grove" is passed to ‘"new()"’, a shallow
    copy of that object will be returned.  A shallow copy
    means that you are returned a new object, but all of the
    objects underneath still refer to the original objects.

Ken MacLeod, ken@bitsko.slc.ut.us

perl(1)