PHP function to set the default value as an object

Question

A function (actually the constructor of another class) needs an object of class temp as argument. So I define interface itemp and include itemp $obj as the function argument. This is fine, and I must pass class temp objects to my function. But now I want to set default value to this itemp $obj argument. How can I accomplish this?

Or is it not possible?

The test code to clarify:

interface itemp { public function get(); }

class temp implements itemp
{
    private $_var;
    public function __construct($var = NULL) { $this->_var = $var; }
    public function get() { return $this->_var ; }
}
$defaultTempObj = new temp('Default');

function func1(itemp $obj)
{
    print "Got: " . $obj->get() . " as argument.\n";
}

function func2(itemp $obj = $defaultTempObj) //error : unexpected T_VARIABLE
{
    print "Got: " . $obj->get() . " as argument.\n";
}

$tempObj = new temp('foo');

func1($defaultTempObj); // Got: Default as argument.
func1($tempObj); // Got : foo as argument.
func1(); // "error : argument 1 must implement interface itemp (should print Default)"
//func2(); // Could not test as I can't define it

You could use my tiny library ValueResolver in this case, check my answer, please — Victor Bocharsky
– Victor Bocharsky, Commented Jul 9, 2015 at 11:06

Arnaud Le Blanc · Accepted Answer · 2011-08-15 12:41:30Z

32

You can't. But you can easily do that:

function func2(itemp $obj = null)
    if ($obj === null) {
        $obj = new temp('Default');
    }
    // ....
}

answered Aug 15, 2011 at 12:41

Arnaud Le Blanc

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1 Comment

wadkar Over a year ago

thanks found this after searching for php method defaults, didn't think that I can compare object with nulls.

JSowa · Accepted Answer · 2023-11-27 15:14:34Z

7

PHP 8.1

Since PHP 8.1 you are able to define a new instance of an object as a default value of the function argument without error, however with some limitations.

function someFunction(Item $obj = new Item('Default'))
{
    ...
}

Documentation: PHP RFC: New in initializers

edited Nov 27, 2023 at 15:14

answered Jul 14, 2021 at 11:06

JSowa

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Comments

Peter Mortensen · Accepted Answer · 2022-01-10 18:28:44Z

4

A possible problem with Arnaud Le Blanc's answer is that in some cases you might wish to allow NULL as a specified parameter, e.g. you might wish for the following to be handled differently:

func2();
func2(NULL);

If so, a better solution would be:

function func2(itemp $obj = NULL)
{

  if (0 === func_num_args())
  {
    $obj = new temp('Default');
  }

  // ...

}

edited Jan 10, 2022 at 18:28

Peter Mortensen

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answered Dec 4, 2014 at 12:01

Michael

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3 Comments

Rangad Over a year ago

Does this make sense? The only valid parameter values are null and implementations of itemp. There is (or atleast should be from an API perspective) no behavorial difference in passing a marker for an absent value (null) and no value at all. I agree, if the parameter would not be typehinted, this is actually usefull in some cases.

Michael Over a year ago

If you're not passing a parameter then you're doing so intentionally, and so you might want it to perform some default behaviour. If you're passing a NULL parameter then it's likely expecting an itemp implementation and so you might want it to log an error and/or throw an exception.

VolkerK Over a year ago

sneaky, that way you're introducing a bit of overloading to php. I like it. Not sure if I'd endorse it, but who cares... :)

Peter Mortensen · Accepted Answer · 2022-01-10 18:30:43Z

2

Since PHP 5.5 you can simply use the ::class to pass a class as a parameter as follow:

function func2($class = SomeObject::class) {
    $object = new $class;
}

func2(); // Will create an instantiation of SomeObject class
func2(AnotherObject::class); // Will create an instantiation of the passed class

edited Jan 10, 2022 at 18:30

Peter Mortensen

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answered Jul 15, 2017 at 20:54

hassan

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1 Comment

Den Over a year ago

Thanks! Sadly it doesn't work together with a type hint: function func2(SomeInterface $class = SomeObject::class) yields a Fatal: "Default value for parameters with a class type can only be NULL" (Tested with PHP 7.2)

Victor Bocharsky · Accepted Answer · 2015-07-09 11:07:26Z

0

You could use my tiny library ValueResolver in this case, for example:

function func2(itemp $obj = null)
    $obj = ValueResolver::resolve($obj, new temp('Default'));
    // ....
}

and don't forget to use namespace use LapaLabs\ValueResolver\Resolver\ValueResolver;

There are also ability to typecasting, for example if your variable's value should be integer, so use this:

$id = ValueResolver::toInteger('6 apples', 1); // returns 6
$id = ValueResolver::toInteger('There are no apples', 1); // returns 1 (used default value)

Check the docs for more examples

answered Jul 9, 2015 at 11:07

Victor Bocharsky

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