(PECL runkit >= 0.7.0)
runkit_function_redefine — Replace a function definition with a new implementation
$funcname
   , string $arglist
   , string $code
   )Note: By default, only userspace functions may be removed, renamed, or modified. In order to override internal functions, you must enable the runkit.internal_override setting in php.ini.
funcnameName of function to redefine
arglistNew list of arguments to be accepted by function
codeNew code implementation
   Returns TRUE on success or FALSE on failure.
  
Example #1 A runkit_function_redefine() example
<?php
function testme() {
  echo "Original Testme Implementation\n";
}
testme();
runkit_function_redefine('testme','','echo "New Testme Implementation\n";');
testme();
?>
The above example will output:
Original Testme Implementation New Testme Implementation