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Designing Interfaces in PHP

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Code to Multiple Interfaces

4:04 with Alena Holligan

Often when working with interfaces, you will be using existing interfaces such as the built-in Iterator interface. By combining multiple interfaces we can build powerful components that can be easily understood by the rest of our application.

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    [MUSIC] 0:00
    Now that we have some data to work with, we want to create a collection that we can 0:05
    use for loops and perform some additional functionalities. 0:09
    For the looping capabilities, PHP offers us an iterator interface, so 0:13
    we don't need to create our own. 0:18
    Often, when working with interfaces, 0:22
    you will use existing interfaces such as the iterator. 0:23
    Besides the interfaces that are built into PHP, 0:28
    most frameworks include their own interfaces. 0:32
    These interfaces work as a kind of guaranteed documentation for 0:35
    using individual components. 0:39
    By combining multiple interfaces, we can build powerful components 0:41
    that can be easily understood by the rest of our application. 0:46
    Let's go back into our collection file. 0:50
    We are going to use implements Iterator. 0:52
    This implements the built in iterator interface. 0:57
    This implements keyword is how we specify that our class 1:01
    will meet the contract of a given interface. 1:06
    We add the name of the interface and 1:09
    then it's up to us to implement the details of that interface's methods. 1:11
    Somewhere in this class, I mentioned that we can combine interfaces together 1:16
    to give our class more and more capabilities. 1:20
    We can do that by adding more interface names separated by comma. 1:24
    So for this example, we also want the collection to be countable, so 1:28
    we can add a comma and then the built-in Countable. 1:33
    We'll use two properties, 1:36
    protected $repo; and a public $collection;. 1:39
    Then we'll set up a construct. 1:48
    On construct, we're going to pass the $repo and 1:50
    optionally the ID and field if we want to limit our collection. 1:53
    We don't care where the data is coming from, but we do need to know that we can 1:58
    access the find and all methods that we set up in our repository interface. 2:02
    Type declarations, also called type hinting, 2:08
    allows us to require a specific type of parameter on a method call. 2:11
    Type hinting for classes and 2:16
    interfaces was added in PHP5 along with arrays and callable. 2:18
    PHP7 added scaler type hints. 2:22
    These are the basic variable types of Boolean, float, integer and string. 2:25
    To specify that our first parameter must 2:30
    implement the repository interface, 2:35
    we specify the name of the interface before the parameter, 2:40
    public function __construct( 2:47
    RepositoryInterface, and then $repo, 2:51
    then we can add our optional parameters, 2:56
    $id = null, $field = 'id'). 3:01
    On construct, we first set the local $repo, 3:06
    then we populate our collection $this -> repo = $repo; if the ID is not empty. 3:11
    Then we're going to say $this -> 3:23
    collection = $this->repo-> find(. 3:28
    We're going to past posts, 3:35
    the ID and the field. 3:40
    Else. 3:44
    $this->collection = $this-> 3:47
    repo->all('posts');. 3:54
    Now we need to implement the methods from the iterator and countable interfaces. 4:00

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