(PECL apd >= 0.2)
override_function — Overrides built-in functions
$function_name
   , string $function_args
   , string $function_code
   )Overrides built-in functions by replacing them in the symbol table.
function_nameThe function to override.
function_argsThe function arguments, as a comma separated string.
       Usually you will want to pass this parameter, as well as the 
       function_code parameter, as a single quote 
       delimited string. The reason for using single quoted strings, is to
       protect the variable names from parsing, otherwise, if you use double
       quotes there will be a need to escape the variable names, e.g. 
       \$your_var.
      
function_codeThe new code for the function.
   Returns TRUE on success or FALSE on failure.
  
Example #1 override_function() example
<?php
override_function('test', '$a,$b', 'echo "DOING TEST"; return $a * $b;');
?>