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Manual Reference Pages  -  CONFIG::MODEL::OBJTREESCANNER (3)

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Config::Model::ObjTreeScanner - Scan config tree and perform call-backs for each element or node



version 2.082


 use Config::Model ;

 # define configuration tree object
 my $model = Config::Model->new ;
 $model ->create_config_class (
    name => "MyClass",
    element => [
        [qw/foo bar/] => {
            type => leaf,
            value_type => string
        baz => {
            type => hash,
            index_type => string ,
            cargo => {
                type => leaf,
                value_type => string,

 ) ;

 my $inst = $model->instance(root_class_name => MyClass );

 my $root = $inst->config_root ;

 # put some data in config tree the hard way
 $root->fetch_element(foo)->store(yada) ;
 $root->fetch_element(bar)->store(bla bla) ;
 $root->fetch_element(baz)->fetch_with_id(en)->store(hello) ;

 # put more data the easy way
 my $step = baz:fr=bonjour baz:hr="dobar dan";
 $root->load( step => $step ) ;

 # define leaf call back
 my $disp_leaf = sub {
      my ($scanner, $data_ref, $node,$element_name,$index, $leaf_object) = @_ ;
      $$data_ref .= "disp_leaf called for ". $leaf_object->name.
        " value ".$leaf_object->fetch."\n";
    } ;

 # simple scanner, (print all values)
 my $scan = Config::Model::ObjTreeScanner-> new (
   leaf_cb => $disp_leaf, # only mandatory parameter
 ) ;

 my $result = ;
 $scan->scan_node(\$result, $root) ;
 print $result ;


This module creates an object that will explore (depth first) a configuration tree.

For each part of the configuration tree, ObjTreeScanner object will call one of the subroutine reference passed during construction. (a call-back or a hook)

Call-back and hook routines will be called:
o For each node containing elements (including root node)
o For each element of a node. This element can be a list, hash, node or simple leaf element.
o For each item contained in a node, hash or list. This item can be a simple leaf or another node.
To continue the exploration, these call-backs must also call the scanner. (i.e. perform another call-back). In other words the user’s subroutine and the scanner play a game of ping-pong until the tree is completely explored.

Hooks routines are not required to resume the exploration, i.e. to call the scanner. This will be done after the hook routine has returned.

The scanner provides a set of default callback for the nodes. This way, the user only have to provide call-backs for the leaves.

The scan is started with a call to scan_node. The first parameter of scan_node is a ref that is passed untouched to all call-back. This ref may be used to store whatever result you want.


    new ( ... )

One way or another, the ObjTreeScanner object must be able to find all callback for all the items of the tree. All the possible call-back and hooks are listed below:
leaf callback: leaf_cb is a catch-all generic callback. All other are specialized call-back : enum_value_cb, integer_value_cb, number_value_cb, boolean_value_cb, string_value_cb, uniline_value_cb, reference_value_cb
node callback: node_content_cb , node_dispatch_cb
node hooks: node_content_hook
element callback: All these call-backs are called on the elements of a node: list_element_cb, check_list_element_cb, hash_element_cb, node_element_cb, node_content_cb.
element hooks: list_element_hook, hash_element_hook.
The user may specify all of them by passing a sub ref to the constructor:

   $scan = Config::Model::ObjTreeScanner-> new
   list_element_cb => sub { ... },

Or use some default callback using the fallback parameter. Note that at least one callback must be provided: leaf_cb.

Optional parameter:
fallback If set to node, the scanner will provide default call-back for node items. If set to leaf, the scanner will set all leaf callback (like enum_value_cb ...) to string_value_cb or to the mandatory leaf_cb value. fallback callback will not override callbacks provided by the user.

If set to all , the scanner provides fallbacks for leaf and node. By default, all fallback are provided.

auto_vivify Whether to create configuration objects while scanning (default is 1).
check yes, no or skip.

Callback prototypes

    Leaf callback

leaf_cb is called for each leaf of the tree. The leaf callback will be called with the following parameters:

 ($scanner, $data_ref,$node,$element_name,$index, $leaf_object)

o $scanner is the scanner object.
o $data_ref is a reference that is first passed to the first call of the scanner. Then $data_ref is relayed through the various call-backs
o $node is the node that contain the leaf.
o $element_name is the element (or attribute) that contain the leaf.
o $index is the index (or hash key) used to get the leaf. This may be undefined if the element type is scalar.
o $leaf_object is a Config::Model::Value object.

    List element callback

list_element_cb is called on all list element of a node, i.e. call on the list object itself and not in the elements contained in the list.

 ($scanner, $data_ref,$node,$element_name,@indexes)

@indexes is a list containing all the indexes of the list.


  sub my_list_element_cb {
     my ($scanner, $data_ref,$node,$element_name,@idx) = @_ ;

     # custom code using $data_ref

     # resume exploration (if needed)
     map {$scanner->scan_list($data_ref,$node,$element_name,$_)} @idx ;

     # note: scan_list and scan_hash are equivalent

    List element hook

list_element_hook: Works like the list element callback. Except that the calls to scan_list are not required. This will be done once the hook returns.

    Check list element callback

check_list_element_cb: Like list_element_cb, but called on a check_list element.

 ($scanner, $data_ref,$node,$element_name,@check_items)

@check_items is a list containing all the items of the check_list.

    Hash element callback

hash_element_cb: Like list_element_cb, but called on a hash element.

 ($scanner, $data_ref,$node,$element_name,@keys)

@keys is an list containing all the keys of the hash.


  sub my_hash_element_cb {
     my ($scanner, $data_ref,$node,$element_name,@keys) = @_ ;

     # custom code using $data_ref

     # resume exploration
     map {$scanner->scan_hash($data_ref,$node,$element_name,$_)} @keys ;

    Hash element hook

hash_element_hook: Works like the hash element callback. Except that the calls to scan_hash are not required. This will be done once the hook returns.

    Node content callback

node_content_cb: This call-back is called foreach node (including root node).

 ($scanner, $data_ref,$node,@element_list)

@element_list contains all the element names of the node.


  sub my_content_cb {
     my ($scanner, $data_ref,$node,@element) = @_ ;

     # custom code using $data_ref

     # resume exploration
     map {$scanner->scan_element($data_ref, $node,$_)} @element ;

    Node content hook

node_content_hook: This hook is called foreach node (including root node). Works like the node content call-back. Except that the calls to scan_element are not required. This will be done once the hook returns.

    Dispatch node callback

node_dispatch_cb: Any callback specified in the hash will be called for each instance of the specified configuration class. (this may include the root node).

For instance, if you have:

  node_dispach_cb => {
    ClassA => \&my_class_a_dispatch_cb,
    ClassB => \&my_class_b_dispatch_cb,

&my_class_a_dispatch_cb will be called for each instance of ClassA and &my_class_b_dispatch_cb will be called for each instance of ClassB.

They will be called with the following parameters:

 ($scanner, $data_ref,$node,@element_list)

@element_list contains all the element names of the node.


  sub my_class_a_dispatch_cb = {
     my ($scanner, $data_ref,$node,@element) = @_ ;

     # custom code using $data_ref

     # resume exploration
     map {$scanner->scan_element($data_ref, $node,$_)} @element ;

    Node element callback

node_element_cb is called for each node contained within a node (i.e not with root node). This node can be held by a plain element or a hash element or a list element:

 ($scanner, $data_ref,$node,$element_name,$key, $contained_node)

$key may be undef if $contained_node is not a part of a hash or a list. $element_name and $key specifies the element name and key of the the contained node you want to scan. (passed with $contained_node) Note that $contained_node may be undef if auto_vivify is 0.


  sub my_node_element_cb {
    my ($scanner, $data_ref,$node,$element_name,$key, $contained_node) = @_;

    # your custom code using $data_ref

    # explore next node


    scan_node ($data_r,$node)

Explore the node and call either node_dispatch_cb (if the node class name matches the dispatch_node hash) <B>orB> (e.g. xor) node_element_cb passing all element names.

After the first callback has returned, up_cb will be called.


Explore the element and call either hash_element_cb, list_element_cb, node_content_cb or a leaf call-back (the leaf call-back called depends on the Value object properties: enum, string, integer and so on)

    scan_hash ($data_r,$node,$element_name,$key)

Explore the hash member (or hash value) and call either node_content_cb or a leaf call-back.

    scan_list ($data_r,$node,$element_name,$index)

Just like scan_hash: Explore the list member and call either node_content_cb or a leaf call-back.

get_keys ($node, CW$element_name)

Returns an list containing the sorted keys of a hash element or returns an list containing (0.. last_index) of an list element.

Throws an exception if element is not an list or a hash element.


Dominique Dumont, (ddumont at cpan dot org)


Config::Model,Config::Model::Node,Config::Model::Instance, Config::Model::HashId, Config::Model::ListId, Config::Model::CheckList, Config::Model::Value


Dominique Dumont


This software is Copyright (c) 2005-2016 by Dominique Dumont.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999

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