PHP and the Strategy pattern. Undefined variable when trying to set a property in the constructor

Question

I'm new to PHP but come from a Java background and I'm trying to implement a simple strategy pattern in OO-PHP.

I'm having a problem with variable scope and assigning an object to a class property. I get an error saying that the property $strategy is undefined when trying to access from the metric constructor. Can anyone help?

Thanks, John

Strategy Pattern Code:

interface iMetric{

    public function calculateReadability($text);

}

/*Context - strategy pattern.*/
class metric{

    private $strategy;

    function __construct($metric){
        $this->$strategy = $metric;
    }

    function calculateReadability($text){

        return $this->$strategy->calculateReadability($text);
    }
}

Where this is being constructed/called from: class fleschEase implements iMetric{

    function calculateReadability($text){
        require_once('textstats/TextStatistics.php');
        $statistics = new TextStatistics();
        return $statistics->flesch_kincaid_reading_ease($text);
    }
}

require_once('metrics.php');

// Flesch Reading Ease
if(strlen($fleschReadingEase)==0){
    $metric = new metric(new fleschEase());
    $fleschReadingEase = $metric->calculateReadability($content);
}

Answer 1

This is a syntax issue, try this:

function __construct($metric){
    $this->strategy = $metric;
}

Properties in PHP have the dollar when they are defined but not when they are used.