Using an array as a default parameter in a PHP function - php

Question

Is it possible to use an array as a default parameter in a PHP function?
I would like to do the following:
$arr = array(1,2,3,4);
function sample($var1, $var2, $var3 = $arr){
echo $var1.$var2;
print_r($var3);
}
sample('a','b');
// Should still work without the third parameter and default to $arr

Answer 1

No, this is not possible, the right hand expression of the default value must be a constant or array literal, i.e.
function sample($var1, $var2, $var3 = array(1, 2, 3, 4))
{
}
If you want this behaviour, you could use a closure:
$arr = array(1, 2, 3, 4);
$sample = function ($var1, $var2, array $var3 = null) use ($arr) {
if (is_null($var3)) {
$var3 = $arr;
}
// your code
}
$sample('a', 'b');
You could also express it with a class:
class Foo
{
private static $arr = array(1, 2, 3, 4);
public static function bar($var1, $var2, array $var3 = null)
{
if (is_null($var3)) {
$var3 = self::$arr;
}
// your code here
}
}
Foo::bar('a', 'b');

Answer 2

You can't pass $arr into the function definition, you'll have to do:
function sample($var1, $var2, $var3 = array('test')){
echo $var1.$var2;
echo print_r($var3);
}
sample('a','b'); // output: abArray ( [0] => test ) 1
or, if you want to be really dirty (I wouldn't recommend it..):
$arr = array('test');
function sample($var1, $var2, $var3 = null){
if($var3 == null){
global $arr;
$var3 = $arr;
}
echo $var1.$var2;
echo print_r($var3);
}
sample('a','b');

Answer 3

(It might not be a complete answer, but it covers some useful cases.)
If you want to get one or more options using an array as an argument in a function (or a method), setting a default set of options might not help. Instead, you can use array_replace().
For example, let's consider a sample $options argument which gets an array with two keys, count and title. Setting a default value for that argument leads overriding it when using the function with any custom $option value passed. In the example, if we set $options to have only one count key, then the title key will be removed. One of the right solutions is the following:
function someCoolFunc($options = []) {
$options = array_replace([
"count" => 144,
"title" => "test"
], $options);
// ...
}
In the example above, you will be ensured that count and title indexes are present, even if the user supplies an empty array (keep in mind, the order of the arguments in array_replace() function is important).
Note: In the explained case, using a class (or interface) is also an option, but one reason to choose arrays over it might be simplicity (or even performance).

Answer 4

I tried the last example above. Here was my comparable test:
function someFunc($options = [])
{
$options = array_replace([
"<br>", "<b>", "<i>", "<u>", "<hr>", "<span>"
], $options);
print_r($options);
}
here is the result:
>>> somefunc()
Array
(
[0] => <br>
[1] => <b>
[2] => <i>
[3] => <u>
[4] => <hr>
[5] => <span>
)
=> null
Yet looks what happens when you try to add a tag. Notice what happens to the original values. Element [0] is changed. The array is not added to:
>>> someFunc(["<div>"])
Array
(
[0] => <div>
[1] => <b>
[2] => <i>
[3] => <u>
[4] => <hr>
[5] => <span>
)
=> null
This would allow you to add an element to default option:
function someFunc($options = array())
{
array_push($options, "<br>", "<b>", "<i>", "<u>", "<hr>", "<span>");
return $options;
}
Here is what results:
>>> someFunc()
=> [
"<br>",
"<b>",
"<i>",
"<u>",
"<hr>",
"<span>",
]
---
someFunc(["<div>","<table>"]);
=> [
"<div>",
"<table>",
"<br>",
"<b>",
"<i>",
"<u>",
"<hr>",
"<span>",
]
this way, the default values get added to.