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 element, 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 children
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 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.
RESERVED NAMES¶
The hash keys `"Contents"' and `"Name"' are used to indicate
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>
