Can use a function when defining a protected class variable

[whitburn]

Apologies if this is a very simple question, as the problem highlights itself as a compiler error. I'm a self taught PHP programmer, so I'm probably misunderstanding something from the object orientated side of things - but despite some googling, it's got me stumped as to how to get around it.

 

I came across the issue when I had to make some fixes to someone else's phpunit code. They had a protected array in a class with one of the key values set as XML text. However, I found that it needed to be converted to a SimpleXMLElement. So I tried converting using simplexml_load_string(). However, this just resulted in the syntax error:

 

       PHP Parse error:  syntax error, unexpected '(', expecting ')'

 

I didn't understand this, so I stripped down to a simple standalone example which replicates the problem:

<?php
class problemDemo
{
    protected $Len = strlen('MY_TEXT');
}
?>

So can anyone explain why I can't set a protected variable value within a class using a function? Is there any alternative way to get around?

 

 

PS. Apologies for post subject - it should have said "CAN'T use a function when defining a protected class variable"!

Edited September 28, 2015 by whitburn

[Jacques1]

Initialization values of properties are evaluated at compile-time, so you can't use arbitrary expressions (you're mostly limited to constant values).

 

To get around this, you can use a constructor to set the property value when the object is created:

<?php



class Demo
{
    protected $len;

    public function __construct()
    {
        $this->len = strlen('MY_TEXT');
    }

    public function getLen()
    {
        return $this->len;
    }
}


$demo = new Demo();
var_dump($demo->getLen());

[hansford]

Class properties can only be assigned a constant value and cannot rely on run-time evaluations. So, no returning values from functions.

[whitburn]

Thanks, that explains my misunderstanding   I'll give it a try.