note 62803 added to functions.arguments

In function calls, PHP clearly distinguishes between missing arguments and present but empty arguments. Thus: <?php function f( $x = 4 ) { echo $x . "\\n"; } f(); // prints 4 f( null ); // prints blank line f( $y ); // $y undefined, prints blank line ?> The utility of the optional argument feature is thus somewhat diminished. Suppose you want to call the function f many times from function g, allowing the caller of g to specify if f should be called with a specific value or with its default value: <?php function f( $x = 4 ) {echo $x . "\\n"; } // option 1: cut and paste the default value from f's interface into g's function g( $x = 4 ) { f( $x ); f( $x ); } // option 2: branch based on input to g function g( $x = null ) { if ( !isset( $x ) ) { f(); f() } else { f( $x ); f( $x ); } } ?> Both options suck. The best approach, it seems to me, is to always use a sentinel like null as the default value of an optional argument. This way, callers like g and g's clients have many options, and furthermore, callers always know how to omit arguments so they can omit one in the middle of the parameter list. <?php function f( $x = null ) { if ( !isset( $x ) ) $x = 4; echo $x . "\\n"; } function g( $x = null ) { f( $x ); f( $x ); } f(); // prints 4 f( null ); // prints 4 f( $y ); // $y undefined, prints 4 g(); // prints 4 twice g( null ); // prints 4 twice g( 5 ); // prints 5 twice ?> ---- Server IP: 66.163.161.117 Probable Submitter: 207.171.180.101 ---- X-Spam-Status: No, hits=3.1 required=5.0 tests=DATE_MISSING,FROM_NO_LOWER autolearn=no version=2.64 ---- Manual Page -- http://www.php.net/manual/en/functions.arguments.php Edit -- http://master.php.net/note/edit/62803 Del: integrated -- http://master.php.net/note/delete/62803/integrated Del: useless -- http://master.php.net/note/delete/62803/useless Del: bad code -- http://master.php.net/note/delete/62803/bad+code Del: spam -- http://master.php.net/note/delete/62803/spam Del: non-english -- http://master.php.net/note/delete/62803/non-english Del: in docs -- http://master.php.net/note/delete/62803/in+docs Del: other reasons-- http://master.php.net/note/delete/62803 Reject -- http://master.php.net/note/reject/62803 Search -- http://master.php.net/manage/user-notes.php