How to pass specific variable in PHP function

I have a PHP function that requires can take 3 parameteres... I want to pa开发者_JAVA技巧ss it a value for the 1st and 3rd parameters but I want the 2nd one to default...

How can I specify which ones I am passing, otherwise its interpreted as me passing values for the 1st and 2nd slots.

Thanks.

You cannot "not pass" a parameter that's not at the end of the parameters list :

• if you want to specify the 3rd parameter, you have to pass the 1st and 2nd ones
• if you want to specify the 2nd parameter, you have to pass the 1st one -- but the 3rd can be left out, if optionnal.

In your case, you have to pass a value for the 2nd parameter -- the default one, ideally ; which, yes, requires your to know that default value.

A possible alternative would be not have your function take 3 parameters, but only one, an array :

function my_function(array $params = array()) {
    // if set, use $params['first']
    // if set, use $params['third']
    // ...
}

And call that function like this :

my_function(array(
    'first' => 'plop',
    'third' => 'glop'
));

This would allow you to :

• accept any number of parameters
• all of which could be optionnal

But :

• your code would be less easy to understand, and the documentation would be less useful : no named parameters
• your IDE would not be able to give you hints on which parameters the function accepts

Once you've defined a default parameter, all the parameters after that one cannot be required. You could do something like:

const MY_FUNCTION_DEFAULT = "default";

public function myFunction($one, $two = "default", $three = 3)
{
   if (is_null($two)) $two = self::MY_FUNCTION_DEFAULT;
   //...
}

// call
$this->myFunction(1, null, 3);

You might also define an empty parameter set and use func_get_args to pull in parameters and analyze those using instanceof or typeof/gettype for type checking if your function is simple enough.

You could use ReflectionFunction. This problem has already been solved by an anonymous contributor at php.net, see orinal here: http://www.php.net/manual/en/function.call-user-func-array.php#66121

For those wishing to implement call-by-name functionality in PHP, such as implemented e.g. in DB apis, here's a quick-n-dirty version for PHP 5 and up

function call_user_func_named($function, $params)
{
    // make sure we do not throw exception if function not found: raise error instead...
    // (oh boy, we do like php 4 better than 5, don't we...)
    if (!function_exists($function))
    {
        trigger_error('call to unexisting function '.$function, E_USER_ERROR);
        return NULL;
    }
    $reflect = new ReflectionFunction($function);
    $real_params = array();
    foreach ($reflect->getParameters() as $i => $param)
    {
        $pname = $param->getName();
        if ($param->isPassedByReference())
        {
            /// @todo shall we raise some warning?
        }
        if (array_key_exists($pname, $params))
        {
            $real_params[] = $params[$pname];
        }
        else if ($param->isDefaultValueAvailable()) {
            $real_params[] = $param->getDefaultValue();
        }
        else
        {
            // missing required parameter: mark an error and exit
            //return new Exception('call to '.$function.' missing parameter nr. '.$i+1);
            trigger_error(sprintf('call to %s missing parameter nr. %d', $function, $i+1), E_USER_ERROR);
            return NULL;
        }
    }
    return call_user_func_array($function, $real_params);
}

function ($foo, $mate, $bar = "") {
  // ... some code
}