Using constants as default function values in PHP

Question

Is this legal?

<?php

function ftw($foo = 'pwnage', $nub = MENU_DEFAULT_VALUE, $odp = ODP_DEFAULT_VALUE) {
      //lots_of_awesome_code
}

?>

where MENU_DEFAULT_VALUE and ODP_DEFAULT_VALUE are constants defined previously in the file.

yeah, but I was having problems in a function that uses this and I thought maybe it was technically possible but against best practices. — Nick Heiner
– Nick Heiner, Commented Aug 5, 2009 at 4:27

zombat · Accepted Answer · 2009-08-04 18:09:26Z

34

Yes, that is legal.

From the manual:

The default value must be a constant expression, not (for example) a variable, a class member or a function call.

Constants fit that bill perfectly.

answered Aug 4, 2009 at 18:09

zombat

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2 Comments

Kamafeather Over a year ago

Any reason/documentation for not being able to refer to the constant using static but just via self, when setting defaults for a class method argument?

nburr Over a year ago

@Kamafeather static is subject to late static bindings, making it inconstant.

BadHorsie · Accepted Answer · 2016-08-01 16:00:16Z

22

In an OOP context, you can also use a class member constant as a default method argument value.

class MyClass
{
    const A = 1;

    public function __construct($arg = self::A)
    {
        echo $arg;
    }
}

answered Aug 1, 2016 at 16:00

BadHorsie

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Comments

Pascal MARTIN · Accepted Answer · 2009-08-04 18:08:43Z

9

why don't you try ?

Still, just in case you can test right now, the following code :

define('MENU_DEFAULT_VALUE', 10);
define('ODP_DEFAULT_VALUE', 'hello');

function ftw($foo = 'pwnage', $nub = MENU_DEFAULT_VALUE, $odp = ODP_DEFAULT_VALUE) {
    var_dump($foo);
    var_dump($nub);
    var_dump($odp);
}

ftw();

gives this output :

string 'pwnage' (length=6)
int 10
string 'hello' (length=5)

So I'd say that, yes, it is valid :-)

answered Aug 4, 2009 at 18:08

Pascal MARTIN

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1 Comment

Kamafeather Over a year ago

In the context of a class method I found out that is not possible to refer to the constant via static, but just using self; this myMethod($arg1 = static::MY_CONST) won't work. Do you know any valid explanation for this different behaviour?

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