PHP - Set class variable from another class variable within same class?

Question

I'm trying to set up a PHP class:

class SomeClass {
    private $tags = array(
        'gen1' => array('some string', 1), 
        'gen2' => array('some string', 2), 
        'gen3' => array('some string', 3), 
        'gen4' => array('some string', 4), 
        'gen5' => array('some string', 5), 
    );

    private $otherVar = $tags['gen1'][0];
}

But this throws the error:

PHP Parse error: syntax error, unexpected '$tags'

Switching it to the usual...

private $otherVar = $this->tags['gen1'][0];

returns the same error:

PHP Parse error: syntax error, unexpected '$this'

But accessing the variable within a function is fine:

private $otherVar;

public function someFunct() {
    $this->otherVar = $this->tags['gen1'][0];
}

How can I use the previously defined class variable to define and initialize the current one, without an additional function?

Answer 1

The closest way to do what you desire is to put the assignment in the constructor. For example:

class SomeClass {
    private $tags = array(
        'gen1' => array('some string', 1), 
        'gen2' => array('some string', 2), 
        'gen3' => array('some string', 3), 
        'gen4' => array('some string', 4), 
        'gen5' => array('some string', 5), 
    );

    private $otherVar;

    function __construct() {
         $this->otherVar = $this->tags['gen1'][0];
    }

    function getOtherVar() {
        return $this->otherVar;
    }
}

$sc = new SomeClass();
echo $s->getOtherVar(); // echoes some string