如何获取可选参数的默认值

Question

Probably this is a limitation of PHP, but is it possible somehow, to call a function - and enforcing the 'default' value of an optional parameter - even if in the function call, the optional parameter is given (and == null )?

Maybe it's easier to show what I mean:

<?php
    function funcWithOptParam($param1, $param2 = 'optional') {
        print_r('param2: ' . $param2);
    }

    funcWithOptParam('something'); // this is the behaviour I want to reproduce

    // this will result in 'param2: optional'

    funcWithOptParam('something', null); // i want $param2 to be 'optional', not null

    // this will result in 'param2: ' instead of 'param2: optional'
?>

Now, the easiest answer to this is "dont write null then" - but in my special case, I get a parameter array for a function call, and only can do this:

<?php
    funcWithOptParam($param[0], $param[1]);
?>

So even if $param[1] is null , the null will overwrite the default value of the optional parameter

I only see one solution to this - to skip the optional parameters, and do it like this:

<?php
    function funcWithOptParam($something, $notOptional) {
         if($notOptional === null) {
              $notOptional = 'defaultvalue';
         }

         ...
    }
?>

But I would like to know if there's another solution to this. Is there a 'real' null value in PHP? That really translates into 'nothing'? Something like undefined in js?

Answer 1

Why not pass the whole array as the function argument? You simply call it this way:

funcWithOptParams($params);

And handle it like so:

function funcWithOptParams($params) {
     if(!isset($params[1])) {
          $params[1] = 'defaultvalue';
     }

     ...
}

This approach gives you the possibility to pass only the arguments you want to specify and have default values in the ones you don't want to specify. As a bonus you don't have to worry about the order of the arguments.

Answer 2

You can use func_num_args & func_get_args to create the behavior you want

function funcWithArbitraryNumParams(){
  $args = array();
  if(!empty(func_num_args)){
   $args = func_get_args();
  }

  print_r($args);
}

Answer 3

You can get the default value, but it's rather ugly...

$function = new ReflectionFunction('your_function_name');

foreach ($function->getParameters() as $param) {
    echo 'Name: ' . $param->getName() . PHP_EOL;
    if ($param->isOptional()) {
        echo 'Default value: ' . $param->getDefaultValue() . PHP_EOL;
    }
    echo PHP_EOL;
}

CodePad .

You could check if the arguments are NULL , and if so, replace them with the default value.