Access a static variable in a class - php

Question

The example below has a syntax error because of the following code:
"another_key" => [ 2 => self::$someStr ]
Using something such as:
"another_key" => [ 2 => "bar" ]
Is correct syntax. Is there any way to access $someStr instead of hard coding the string?
<?php
class Foo {
protected static $someStr = 'bar';
private static $arr = [
"some_key" => [ 1 ],
"another_key" => [ 2 => self::$someStr ]
];
}

Answer 1

You cannot access static variables inside of the declaration of other static variables. You can either declare a class constant or initialize it by accessing via a function. A class constant would look like this:
class Foo {
const someStr = 'bar';
private static $arr = [
"some_key" => [ 1 ],
"another_key" => [ 2 => self::someStr ]
];
}
Or using a function:
class Foo {
private static $someStr = 'bar';
private static $arr = [
"some_key" => [ 1 ],
"another_key" => [ 2 => null ]
];
private static function setKey(){
self::$arr['another_key'] = [2 => self::$somStr];
}
}
You'd then have to call Foo::setKey() at some point before accessing the variable.

Answer 2

If you want to access a property to set the value of another property you should be doing it in the class' constructor. Something like this:
class Foo {
protected static $someStr = 'bar';
private static $arr = [
'some_key' => [1]
];
public function __constructor()
{
self::arr['another_key'] = [2 => self::$somStr];
}
}
For this to work you will need to instantiate your class.
You can view some examples on property declarations in the PHP documentation.