Doesnt dependency injection hurt SRP? - php

Question

given a class:
class Cart
{
private $items;
public function add (Product $item)
{
$this->items[] = $item;
}
public function clear()
{
$this->items = array();
}
}
this is just cool. But for testing, lets make a possibility to change the items:
class Cart
{
private $items;
public function add (Product $item)
{
$this->items[] = $item;
}
public function clear()
{
$this->items = array();
}
public function setItems ($items)
{
$this->items = $items;
}
public function getItems()
{
return $this->items;
}
}
but I think its not a good solution as the getItems, setItems isnt really related to the class itself. Of course, I can write that:
class Cart extends DI
{
protected $items;
public function add (Product $item)
{
$this->items[] = $item;
}
public function clear()
{
$this->items = array();
}
}
class DI
{
public function setItems ($items)
{
$this->items = $items;
}
public function getItems()
{
return $this->items;
}
}
but what if I have $items and $discounts too? There is no multiple inheritance

Answer 1

Side note: Having a superclass with functions using the protected variables of a subclass is generally bad practice, since inheritance should only go one way, and that way is down, never up. What if someone creates a DI class and then calls a setItems or getItems function? Trouble! Do NOT practice the last example of code.
My answer:
The Setters/Getters ARE related because Cart has the single responsibility of providing functionality towards $items. The way I see it, you do not violate SRP using DI, since all you're doing is defining the dependency outside the class before sending it in, giving $item no reason to change and sharing no responsibility. Your second code example is the correct solution in this case.
Your third example violates SRP since the Cart class shares responsibility of $items with the DI class.
Some links:
See this article for more information about Dependency Injection:
http://tutorials.jenkov.com/dependency-injection/dependency-injection-benefits.html
SRP: https://en.wikipedia.org/wiki/Single_responsibility_principle