withphp5.php

<?php


interface Item {
 
}


interface Collection {
    /**
     *
     * @return $this
     */
    public function addItem(Item $item );
}


class CollectionOne extends Collection{
	
public function addItem(Item $item ) 
  {
    $this->items[] = $item;
    return $this;
  }
	
	
}

class CollectionTwo extends Collection{
	
	public function addItem(Item $item ) 
  {
    $this->items[] = $item;
    return $item; // not correct but no compile time error is thrown
  }
}

withphp7.php

<?php
interface Item {
 
}

interface Collection {
    public function addItem(Item $item ) : Item;
}

 


class CollectionConcrete extends Collection{
	
	public function addItem(Item $item ) : Item 
  {
    $this->items[] = $item;
    return $this;
  }
	
	
}

$collection = ( new CollectionConcrete7() )->addItem($i)->addItem($i2);