Question

我有一套PHP功能,需要3个参数。我想把它当作第1和第3个参数的价值,但我希望第2个参数会落空。

我怎么能具体说明我通过什么,否则,它就被解释为我通过第1和第2个位置的数值。

感谢。

Answer 1

不能“通过”参数,该参数在参数清单末尾:

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.

在你的情况下,你必须给2个参数——最好是缺省——带来价值;如果是,这要求你知道这一缺省价值。

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 ]
    // ...
}

并称之为这一职能:

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

这将使你能够:

accept any number of parameters
all of which could be optionnal

但:

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

Answer 2

一旦确定一个缺省参数,就不需要该参数之后的所有参数。你可以做这样的事情:

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);

http://www.php.net/manual/en/Function.func-get-args.php

Answer 3

你可以使用反思功能。这一问题已经由一位匿名的投稿人解决,见网站:。

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);
}

友情链接