interfaces.php

<?php

interface Template{
 public function setVariable($name, $var);
 public function getVariable();
}

class WorkingTemplate implements Template{

 private $vars = [];
 private $values;
 public function setVariable($name, $var){
 $this->vars[$name] = $var;
 }

 public function getVariable(){
 foreach($this->vars as $name=>$var){
 $this->values .=$var;
 }

 return $this->values;
 }
}

$obj = new WorkingTemplate();

$obj->setVariable(1, "test1");
$obj->setVariable(2, "test2");


var_dump($obj->getVariable());
?>