php function arguments

Question

I don't know how or where I got this idea in my head but for some reason I thought this was possible. Obviously after testing it doesn't work, but is there a way to make it work? I want to set $value2 without having to enter anything at all for $value1.

function test($value1 = 1, $value2 = 2) {
echo 'Value 1: '.$value1.'<br />';
echo 'Value 2: '.$value2.'<br />';
}
test($value2 = 3);
// output
Value 1: 3
Value 2: 2

• Mike Purcell: Unpossible. You really want this behavior, switch args 1 and 2 in the signature.
• Raphael Michel: Yep, you're looking for keyword arguments which are not available in PHP but e.g. in Python.
• John Flatness: possible duplicate of PHP Using Default Arguments in a Function
• Clint C.: Thanks for all of the answers so far. Yes, the main point was hoping I didn't have to do a work around, but obviously it's not possible. I wonder why this wasn't made possible in php?

Answer 1

Its not entirely possible the way you want.

Simply,

function test($value1 = null, $value2 = 2) {
echo 'Value 1: '.$value1.'<br />';
echo 'Value 2: '.$value2.'<br />';
}
test(NULL, $value2 = 3);

Or, Use array as parameters

function test($array) {
if(isset($array['value1'])) echo 'Value 1: '.$array['value1'].'<br />';
if(isset($array['value2'])) echo 'Value 2: '.$array['value2'].'<br />';
}
test(array('value2' => 3));

---

Update:

My another attempt

function test() {
 $args = func_get_args();
 $count = count($args);
 if($count==1) { test1Arg($args[0]); }
 elseif($count == 2) { test2Arg($args[0],$args[1]); }
 else { //void; }
}
function test1Arg($arg1) {
 //Do something for only one argument
}
function test2Arg($arg1,$arg2) {
 //Do something for two args
}

• Mike Purcell: OP is aware of this solution: "I want to set $value2 without having to enter anything at all for $value1".
• Kristian: +1 for the effort, but the array as a param solution is getting away form the essence of the problem, in my opinion
• Raphael Michel: test(NULL, $value2 = 3); is leading to unwanted behaviour as the $value2 = does something completely different from what the OP is wanting to do and is misleading when being read.
• Raphael Michel: The idea with arrays you edited into this answer is good, sadly I'm unable to change my vote.
• Starx: @rami, I edited, SO you can change your vote, and I updated with another way too.

Answer 2

What you're trying to do is called "keyword arguments" or "named arguments" and is not available in PHP in contrast to other scripting languages like Python.

If you have functions with hundreds of parameters and really want to achieve a more flexible solution than what PHP comes with, you could build your own workaround with arrays or objects, maybe in conjunction with func_get_args(). But this obviously isn't as beautiful as real keyword arguments.

Answer 3

For a simple function, it's likely impractical to jump into OOP; however, to throw more fuel to this variation fire, this is a case where you could probably use OOP, for better or worse.

Default function parameters are unwieldy to swap around for your convenience, however, that's not the case with extended classes. Those are meant to be varied and mutated as the need arises.

class test {
 var $value1 = 1;
 var $value2 = 2;
 function __construct() {
 printf( "Value 1 = %s, value 2 = %s\n", $this->value1, $this->value2 );
 }
}
class test2 extends test {
 var $value2 = 42;
}
$me = new test(); // outputs Value 1 = 1, value 2 = 2
$me2 = new test2(); // outputs Value 1 = 1, value 2 = 42

Once again, not the practical solution for simplest of tasks, but, it will allow you to mutate code fragments at will. Rethink whether you can rewrite your code to take advantage of this style.

Answer 4

function test($value1 = null, $value2 = null) {
 $value1 = $value1 ?: 1;
 $value2 = $value2 ?: 2;
 echo 'Value 1: '.$value1.'<br />';
 echo 'Value 2: '.$value2.'<br />';
}
test(null, 3);

• Raphael Michel: As far as I can see, OP is aware of this solution so I don't think it is what he wants.
• KingCrunch: Thanks for your hint, but thats the way it works, even if the OP doesn't like it.
• Raphael Michel: But it's not what you want if you have a function with fifteen arguments. See my, Starx's or TRiG's answer – I guess in this case an array is the best solution
• KingCrunch: You really have functions/methods with fifteen arguments?!? Oo Sounds like a design flaw :X
• Raphael Michel: I don't. But simetimes it does make sense.

Answer 5

AFAIK, you can't modify the values of the arguments the way you want it. The manual even says this is invalid (http://php.net/manual/en/functions.arguments.php#example-153).

What you're doing withtest($value2 = 3); is first assigning to a new variable $value2 a value of 3 and then sending it as the first parameter of test.

However, you can create a function where when you send a null parameter, it gets a value assigned:

function test($value1 = NULL, $value2 = 2) {
 if ($value1 === NULL)
 $value1 = 1 // $value1 default value
 echo 'Value 1: '.$value1.'<br />';
 echo 'Value 2: '.$value2.'<br />';
}
test(NULL, 3);
// output
Value 1: 1
Value 2: 3

Or well, change the default values of the variables:

function test($value2 = 2, $value1 = 1) {
 echo 'Value 1: '.$value1.'<br />';
 echo 'Value 2: '.$value2.'<br />';
}
test(3);
// output
Value 1: 1
Value 2: 3

Answer 6

This is not possible in PHP, as handy as it would be, but there are a couple of ways around it.

function func($val1=null, $val2=null) {
 // Set default values.
 if (!$val1) $val1 = 1;
 if (!$val2) $val2 = 2;
 // Your code here.
}
func(null, 74); // Uses the default value of 1 for $val1.

Or use an array (much handier if you have a very long list of arguments):

function func($arr) {
 // Set default values.
 $val1 = isset($arr[1]) ? $arr[1] : 1;
 $val2 = isset($arr[2]) ? $arr[2] : 2;
 // Your code here.
}
func(array(2 => 74)); // Uses the default value of 1 for $val1.

Actually, I have a function which takes the array, the key, and the default, and returns a value, so I could write those lines as

$val1 = Core::val($arr, 1, 1); // array, key, default
$val2 = Core::val($arr, 2, 2);

Answer 7

It is considered bad practice to have arguments with default values come after args that do not. the reason being that its not allowed to simply write a function with a bunch of commas in it.

In your case, you should pass a value to both parameters. Even if the value is null.

Answer 8

Maybe this is what u r looking for:

 function test($value1, $value2) 
 {
 if ($value1!="") 
 {
 echo 'Value 1: '.$value1.'<br />'; 
 }
 else
 {
 echo 'Value 1: 3'<br />'; 
 }
 echo 'Value 2: '.$value2.'<br />';
 }
 test("", $value2 = 3);
 // output
 Value 1: 3
 Value 2: 2

• Raphael Michel: As far as I can see, OP is aware of this solution so I don't think it is what he wants (he wants to pass no value vor $value1 AT ALL, which absolutely makes sense if you have a bunch of arguments.)
• dimmat: Rami, thanks for commenting but there is no simpler way. Unfortunately, argument for value1 MUST be given.