You can do some kind of overloading functions in PHP using "function_exists". 

Let's suppose you want a script to call plugins that are php files and you want the plugins to "override" behaviours that if not overriden are used by default.

You might for example write a "mySQL table viewer" which displays a table and it "opens a table", "dumps the header", "dumps row-by-row" and then "closes the table".

Let's suppose you want a plugin for "Stocks" which prints negative stocks in red, so you want to override the "dumping row-by-row" to do that behaviour. Instead you do not want to have all the "default behaviour" repeated in the plugin.

You may then do the following:

1) Define a default plugin (ex: "default.php"

2) Write all your functions in default.php to open, dump and close, but add them a suffix:

open_table_default()
dump_header_default()
dump_row_default()
close_table_default()

3) Call your functions with a wrapper: Insetad of this:
open_table() or open_table_default() write this:

plugincall("open_table");

4) Then write a function called plugincall which uses function_exists() to see if you call one or the other function:

function plugincall($desired_function_name)
{

if( function_exists( $desired_function_name))
{
    //Call the plugin
    //Note the $ before the name
    $desired_function_name()
}
else
{
  $desired_function_name = $desired_function_name . "_default";
  if( function_exists($desired_function_name))
  {
      //Call the default
      //Note the $ before the name
      $desired_function_name()
  }
  else
  {
      // Nor the plugin nor the default were defined
  }
}

So, now, if the require_once(plugin.php) contains a function called "open_table()", it will be used. Instaed, "open_table_default()" will be used.

It's not like overloading functions, but it is very useful to write scripts ampliable by other programmers: If they write a function, it is used, if not, the default is used.

See ya!
Xavier Montero.