<?php

class Test {
    private $var1;
    private $var2;
    private $var3;

    public function __construct($params) {
        foreach($params as $key => $value) {
            $this->$key = $value;
        }
    }
}

$params = array();
$params['var2'] = "Variable 2 Instantiated";
$params['var3'] = "Test";
$test = new Test($params);

var_dump($test);

object(Test)#1 (3) {
  ["var1:private"]=>
  NULL
  ["var2:private"]=>
  string(23) "Variable 2 Instantiated"
  ["var3:private"]=>
  string(4) "Test"
}