Data::Grove::Visitor(3) User Contributed Perl Documentation Data::Grove::Visitor(3)
Data::Grove::Visitor - add visitor/callback methods to Data::Grove objects
@results = $object->accept ($visitor, ...);
@results = $object->accept_name ($visitor, ...);
@results = $object->children_accept ($visitor, ...);
@results = $object->children_accept_name ($visitor, ...);
Data::Grove::Visitor adds visitor methods (callbacks) to Data::Grove objects. A ``visi-
tor'' 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 ele-
ment 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"'
`"children_accept"' calls `"accept"' on each of the children of the element. This is gen-
erally 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. `"chil-
dren_accept_name"' does the same but calling `"accept_name"' on each of the children.
`"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"', `"document"', etc.) of the objects it implements.
The hash keys `"Contents"' and `"Name"' are used to indicate objects with children (for
`"children_accept"') and named objects (for `"accept_name"').
These are random ideas that haven't been implemented yet:
o 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 pack-
age 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.
Ken MacLeod, email@example.com
Extensible Markup Language (XML) <http://www.w3c.org/XML>
perl v5.8.0 2000-02-22 Data::Grove::Visitor(3)