Using Default Arguments in a Function

Question

I am confused about default values for PHP functions. Say I have a function like this:

function foo($blah, $x = "some value", $y = "some other value") {
    // code here!
}

What if I want to use the default argument for $x and set a different argument for $y?

I have been experimenting with different ways and I am just getting more confused. For example, I tried these two:

foo("blah", null, "test");
foo("blah", "", "test");

But both of those do not result in a proper default argument for $x. I have also tried to set it by variable name.

foo("blah", $x, $y = "test");   

I fully expected something like this to work. But it doesn't work as I expected at all. It seems like no matter what I do, I am going to have to end up typing in the default arguments anyway, every time I invoke the function. And I must be missing something obvious.

Answer 1

You can also check if you have an empty string as argument so you can call like:

foo('blah', "", 'non-default y value', null);

Below the function:

function foo($blah, $x = null, $y = null, $z = null) {
    if (null === $x || "" === $x) {
        $x = "some value";
    }

    if (null === $y || "" === $y) {
        $y = "some other value";
    }

    if (null === $z || "" === $z) {
        $z = "some other value";
    }

    code here!

}

It doesn't matter if you fill null or "", you will still get the same result.

Answer 2

The only way I know of doing it is by omitting the parameter. The only way to omit the parameter is to rearrange the parameter list so that the one you want to omit is after the parameters that you HAVE to set. For example:

function foo($blah, $y = "some other value", $x = "some value")

Then you can call foo like:

foo("blah", "test");

This will result in:

$blah = "blah";
$y = "test";
$x = "some value";

Answer 3

function image(array $img)
{
    $defaults = array(
        'src'    => 'cow.png',
        'alt'    => 'milk factory',
        'height' => 100,
        'width'  => 50
    );

    $img = array_merge($defaults, $img);
    /* ... */
}

Answer 4

You can't do this directly, but a little code fiddling makes it possible to emulate.

function foo($blah, $x = false, $y = false) {
  if (!$x) $x = "some value";
  if (!$y) $y = "some other value";

  // code
}