Question

According to the Law of Demeter, can you call methods on returned objects?

E.g.

<?php
class O
{
    public function m($http)
    {
        $response = $http->get('http://www.google.com');
        return $response->getBody(); // violation?
    }
}
?>

$http->get() returns an object. Does this count as an object created/instantiated within M? If you can not call methods on it (according to LoD), how would you handle this situation?

Answer 1

This is not a violation of the Law of Demeter, given:

More formally, the Law of Demeter for
functions requires that a method M of
an object O may only invoke the
methods of the following kinds of
objects:

• O itself
• M’s parameters
• any objects created/instantiated within M
• O’s direct component objects
• a global variable, accessible by O, in the scope of M

Since $response is an object that is created within M, you can invoke a method upon that object without violation. However, it would be a violation to access properties beyond getBody():

$length = $response->getBody()->length;

Sometimes you can say that the law can be simplified by saying it’s the “one dot” rule, meaning that you can access one property or method deep.