Entry

How do I pass a user defined function to a class and call it from there?

Aug 25th, 2003 19:16
Perry Keller, dingy,

Passing a function to a function is commonly needed for traversing a 
list or a tree. In this example, I have a class Tree that has a member 
function breadthFirstTravese as follows:

class Tree{
  var $name // string
  var $children // array of Tree
  .
  .
  .

  function breadthFirstTraverse($visit){
    $visit($this);
    if ($this->children != NULL)
      foreach ($this->children as $value)
        $value->breadthFirstTraverse($visit);
  }
  .
  .
  .
}

somewhere else you define the specific function to perform on each node 
for example to print a directory like structure:

function Visit($node){
  $tabstr = "";
  for ($i=0; $i < $node->level; $i++) $tabstr .= "&nbsp;&nbsp;&nbsp;";
  echo "$tabstr $node->name<br />";
}

function Visit2($node){
  // some other process
}

then you can pass the function like this:

$t = new Tree($foo) // whatever variables you need
$func = "Visit";
$t->breadthFirstTraverse($func);
$func = "Visit2";
$t->breadthFirstTraverse($func);