data::grove::visitor(3)
NAME
Data::Grove::Visitor - add visitor/callback methods to
Data::Grove objects
SYNOPSIS
use Data::Grove::Visitor; @results = $object->accept ($visitor, ...); @results = $object->accept_name ($visitor, ...); @results = $object->children_accept ($visitor, ...); @results = $object->children_accept_name ($visitor, ...);
DESCRIPTION
Data::Grove::Visitor adds visitor methods (callbacks) to
Data::Grove objects. A ``visitor'' is a class (a package)
you write that has methods (subs) corresponding to the
objects in the classes being visited. You use the visitor
methods by creating an instance of your visitor class, and
then calling `"accept($my_visitor)"' on the top-most
object you want to visit, that object will in turn call
your visitor back with `"visit_OBJECT"', where OBJECT is
the type of object.
There are several forms of `"accept"'. Simply calling
`"accept"' calls your package back using the object type
of the object you are visiting. Calling `"accept_name"'
on an element object calls you back with
`"visit_name_NAME"' where NAME is the tag name of the ele
ment, on all other objects it's as if you called
`"accept"'.
All of the forms of `"accept"' return a concatenated list
of the result of all `"visit"' methods.
`"children_accept"' calls `"accept"' on each of the chil
dren of the element. This is generally used in element
callbacks to recurse down into the element's children, you
don't need to get the element's contents and call
`"accept"' on each item. `"children_accept_name"' does
the same but calling `"accept_name"' on each of the chil
dren. `"attr_accept"' calls `"accept"' on each of the
objects in the named attribute.
Refer to the documentation of the classes you are visiting
(XML::Grove, etc.) for the type names (`"element"', `"doc
ument"', etc.) of the objects it implements.
RESERVED NAMES
The hash keys `"Contents"' and `"Name"' are used to indi
cate objects with children (for `"children_accept"') and
named objects (for `"accept_name"').
NOTES
These are random ideas that haven't been implemented yet:
- · Several objects fall into subclasses, or you may want
- to be able to subclass a visited object and still be
able to tell the difference. In SGML::Grove I had
used the package name in the callback
(`"visit_SGML_Element"') instead of a generic name
(`"visit_element"'). The idea here would be to try
calling `"visit_PACKAGE"' with the most specific class
first, then try superclasses, and lastly to try the
generic.
AUTHOR
Ken MacLeod, ken@bitsko.slc.ut.us
SEE ALSO
perl(1), Data::Grove
- Extensible Markup Language (XML) <http://www.w3c.org/XML>