Does PHP allow named parameters so that optional arguments can be omitted from function calls?

No, it is not possible : if you want to pass the third parameter, you have to pass the second one. And named parameters are not possible either.

A "solution" would be to use only one parameter, an array, and always pass it... But don't always define everything in it.

For instance :

function foo($params) {
    var_dump($params);
}

And calling it this way :

foo(array(
    'a' => 'hello',
));

foo(array(
    'a' => 'hello',
    'c' => 'glop',
));

foo(array(
    'a' => 'hello',
    'test' => 'another one',
));

Will get you this output :

array
  'a' => string 'hello' (length=5)

array
  'a' => string 'hello' (length=5)
  'c' => string 'glop' (length=4)

array
  'a' => string 'hello' (length=5)
  'test' => string 'another one' (length=11)

But I don't really like this solution :

• You will lose the phpdoc
• Your IDE will not be able to provide any hint anymore... Which is bad

So I'd go with this only in very specific cases -- for functions with lots of optionnal parameters, for instance...

No, PHP cannot pass arguments by name.

If you have a function that takes a lot of arguments and all of them have default values you can consider making the function accept an array of arguments instead:

function test (array $args) {
    $defaults = array('a' => '', 'b' => '', 'c' => '');
    $args = array_merge($defaults, array_intersect_key($args, $defaults));

    list($a, $b, $c) = array_values($args);
    // an alternative to list(): extract($args);

    // you can now use $a, $b, $c       
}

See it in action.

PHP 8 will be released on November 26, 2020. (Happy Thanksgiving from PHP!)

In this major version release, "named parameters" (aka "named arguments") afford developers some really cool new techniques when calling native and custom functions.

The custom function in this question can now be called with the first parameter (because there is no default for it) and then only the third parameter passed by using named parameters like this: (Demo)

function foo($a, $b = '', $c = '') {
    echo $a . '&' . $b . '&' . $c;
}

foo("hello", c: "bar"); 
// output: hello&&bar

Notice that the second parameter did not need to be declared in the function call because it has a default value defined -- the default value are automatically used within the function.

Part of the beauty of this new feature is that you don't need to be careful about the order of your named parameters -- the order of their declaration is irrelevant. foo(c: "bar", a: "hello"); works just the same. Having the ability to "skip" declarations and write declarative parameters will improve the readability of your scripts. The only downside of this new feature is that there will be a little bit more bloat in the function calls, but I (and many others) think the benefits outweigh this "cost".

Here is an example of a native function omitting the limit parameter, writing the parameters out of their normal order, and declaring a reference variable. (Demo)

echo preg_replace(
         subject: 'Hello 7',
         pattern: '/[a-z ]/',
         count: $counted,
         replacement: ''
     )
     . " & " . $counted;
// output: H7 & 5

---

There is more to tell about this new feature. You can even use an associative array to pass the named parameters to the function where the spread/splat operator can be used to unpack the data!

(*notice the slight difference in declaring the reference variable.) (Demo)

$params = [
    'subject' => 'Hello 7',  // normally third parameter
    'pattern' => '/[a-z ]/', // normally first parameter
    // 'limit'               // normally fourth parameter, omitted for this demonstration; the default -1 will be used
    'count' => &$counted,    // normally fifth parameter
    //         ^-- don't forget to make it modifiable!
    'replacement' => '',     // normally second parameter
];
echo preg_replace(...$params) . " & " . $counted;
// same output as the previous snippet

For more information, here are a few leads that explain further about this feature and some common related errors: (I have no affiliation with the following sites)

• https://wiki.php.net/rfc/named_params
• https://stitcher.io/blog/php-8-named-arguments
• https://stitcher.io/blog/why-we-need-named-params-in-php