pass value for last default parameter of function - php

Question

From very long time i am working on php.
But one question may I have no idea about
like I have one function as bellow:
function hello($param1, $param2="2", $param3="3", $param4="4")
Now whenever I will use this function and if I need 4th params thats the $param4 then still I need to call all as blank like this one:
hello(1, '', '', "param4");
So is there any another way to just pass 1st and 4th param in call rather then long list of blanks ?
Or is there any other standard way for this ?

Answer 1

There was an RFC for this named skipparams but it was declined.
PHP has no syntactic sugar such as hello(1, , , "param4"); nor hello(1, default, default, "param4"); (per the RFC) for skipping optional parameters when calling a function.
If this is your own function then you can choose the common jQuery style of passing options into plug-ins like this:
function hello( $param1, $more_params = [] )
{
static $default_params = [
'param2' => '2',
'param3' => '3',
'param4' => '4'
];
$more_params = array_merge( $default_params, $more_params );
}
Now you can:
hello( 1, [ 'param4'=>'not 4, muahaha!' ] );
If your function requires some advanced stuff such as type hinting then instead of array_merge() you will need to manually loop $more_params and enforce the types.

Answer 2

One potential way you can do this, while a little bit hacky, may work well in some situations.
Instead of passing multiple variables, pass a single array variable, and inside the function check if the specific keys exist.
function hello($param1, $variables = ["param2" => "2", "param3" => "3", "param4" => "4"]) {
if(!array_key_exists("param2", $variables)) $variables['param2'] = "2";
if(!array_key_exists("param3", $variables)) $variables['param3'] = "3";
if(!array_key_exists("param4", $variables)) $variables['param4'] = "4";
echo "<pre>".print_r($variables, true)."</pre>";
}
This will allow you to set "param4" in the above variable, while still remaining default on all of the others.
Calling the function this way:
hello("test", ["param4" => "filling in variable 4"]);
Will result in the output being:
Array
(
[param4] => filling in variable 4
[param2] => 2
[param3] => 3
)
I don't generally recommend this if it can be avoided, but if you absolutely need this functionality, this may work for you.
The key here is that you have a specifically named index inside the array being passed, that you can check against inside the function itself.

Answer 3

The answer, as I see it, is yes and no.
No, because there's no way to do this in a standard fashion.
Yes, because you can hack around it. This is hacky, but it works ;)
Example:
function some_call($parm1, $parm2='', $parm3='', $parm4='') { ... }
and the sauce:
function some_call_4($parm1, $parm4) {
return some_call($parm1, '', '', $parm4);
}
So if you make that call ALOT and are tired of typing it out, you can just hack around it.
Sorry, that's all I've got for you.

Answer 4

It is an overhead, but you can use ReflectionFunction to create a class, instance of which that can be invoked with named parameters:
final class FunctionWithNamedParams
{
private $func;
public function __construct($func)
{
$this->func = $func;
}
public function __invoke($params = [])
{
return ($this->func)(...$this->resolveParams($params));
}
private function resolveParams($params)
{
$rf = new ReflectionFunction($this->func);
return array_reduce(
$rf->getParameters(),
function ($carry, $param) use ($params) {
if (isset($params[$param->getName()])) {
$carry[] = $params[$param->getName()];
} else if ($param->isDefaultValueAvailable()) {
$carry[] = $param->getDefaultValue();
} else {
throw new BadFunctionCallException;
}
return $carry;
},
[]
);
}
}
Then you can use it like this:
function hello($param1, $param2 = "2", $param3 = "3", $param4 = "4")
{
var_dump($param1, $param2, $param3, $param4);
}
$func = new FunctionWithNamedParams('hello');
$func(['param1' => '1', 'param4' => 'foo']);
Here is the demo.