1Data::Grove::Visitor(3)User Contributed Perl DocumentatioDnata::Grove::Visitor(3)
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6 Data::Grove::Visitor - add visitor/callback methods to Data::Grove
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10 use Data::Grove::Visitor;
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12 @results = $object->accept ($visitor, ...);
13 @results = $object->accept_name ($visitor, ...);
14 @results = $object->children_accept ($visitor, ...);
15 @results = $object->children_accept_name ($visitor, ...);
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18 Data::Grove::Visitor adds visitor methods (callbacks) to Data::Grove
19 objects. A ``visitor'' is a class (a package) you write that has
20 methods (subs) corresponding to the objects in the classes being
21 visited. You use the visitor methods by creating an instance of your
22 visitor class, and then calling `"accept($my_visitor)"' on the top-most
23 object you want to visit, that object will in turn call your visitor
24 back with `"visit_OBJECT"', where OBJECT is the type of object.
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26 There are several forms of `"accept"'. Simply calling `"accept"' calls
27 your package back using the object type of the object you are visiting.
28 Calling `"accept_name"' on an element object calls you back with
29 `"visit_name_NAME"' where NAME is the tag name of the element, on all
30 other objects it's as if you called `"accept"'.
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32 All of the forms of `"accept"' return a concatenated list of the result
33 of all `"visit"' methods.
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35 `"children_accept"' calls `"accept"' on each of the children of the
36 element. This is generally used in element callbacks to recurse down
37 into the element's children, you don't need to get the element's
38 contents and call `"accept"' on each item. `"children_accept_name"'
39 does the same but calling `"accept_name"' on each of the children.
40 `"attr_accept"' calls `"accept"' on each of the objects in the named
41 attribute.
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43 Refer to the documentation of the classes you are visiting (XML::Grove,
44 etc.) for the type names (`"element"', `"document"', etc.) of the
45 objects it implements.
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48 The hash keys `"Contents"' and `"Name"' are used to indicate objects
49 with children (for `"children_accept"') and named objects (for
50 `"accept_name"').
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53 These are random ideas that haven't been implemented yet:
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55 ยท Several objects fall into subclasses, or you may want to be able to
56 subclass a visited object and still be able to tell the difference.
57 In SGML::Grove I had used the package name in the callback
58 (`"visit_SGML_Element"') instead of a generic name
59 (`"visit_element"'). The idea here would be to try calling
60 `"visit_PACKAGE"' with the most specific class first, then try
61 superclasses, and lastly to try the generic.
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64 Ken MacLeod, ken@bitsko.slc.ut.us
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67 perl(1), Data::Grove
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69 Extensible Markup Language (XML) <http://www.w3c.org/XML>
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73perl v5.30.1 2020-01-30 Data::Grove::Visitor(3)