We needed to modify a shared function to include additional information … but didn’t want to coordinate changing all of the calls to the function as one change. Simplest way to accomplish that was to set a default value for the new parameter — either to NULL and just not do the new thing when the parameter is NULL or some value that indicates that we’re not yet gathering that data.

<?php

function testFunction($strOldParameter, $strNewParameter=NULL){
     echo "The old parameter is |$strOldParameter|\n";
     if($strNewParameter){
          echo "The new parameter is |$strNewParameter|\n";
     }
}

testFunction("first", "second");
testFunction("justFirst");

?>