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Using Objects and Array Keys

Using Objects and Array Keys

Until now, we’ve been working with simple values like pageTitle or products, which is an array that contains simple values where we loop over and print each out. Now, let’s make things a bit more interesting!

Using data from an Array

I’m going to pass in a new variable called pageData:

// index.php
// ...

echo $twig->render('homepage.twig', array(
    'pageData' => array(
        'title'     => 'Suit Up!',
        'summary'   => "You're hip, you're cool, you're a penguin! Now, start dressing like one! Find the latest suits, bow-ties, swim shorts and other outfits here!",
        'hasSale'   => true,
    ),
    // ...
));

If you hadn’t seen the PHP code I just used to create this variable, you could use the handy dump function to see that it’s an array with a title, summary and hasSale keys:

{{ dump(pageData) }}

So how can we get to the data on the keys of the array?

The answer is with the almighty period (.). To print the title, just say pageData.title. To print the summary, use the same trick!

<div class="hero-unit">
    <h1>{{ pageData.title }}</h1>
    <p>
        {{ pageData.summary }}
    </p>
</div>

This can be used anywhere, like in an if statement in exactly the same way:

{% if pageData.hasSale %}
    <div>We're having a sale!</div>
{% endif %}

So if you ever need data from an array, the . operator is your answer!

The much-rarer [] Syntax

The products variable is also an array, but since it’s a collection of items, we loop over it with the for tag instead. But if we did need to manually get the first item, or “zero” key from the array, we can do that. If you’re thinking that you would say products.0, you’re right!

{{ products.0 }}

You may sometimes see another syntax for getting items from an array:

{{ products[0] }}

Don’t let this confuse you - you almost always want to use the period. The square bracket syntax is only needed in some uncommon cases when you need to use a variable as the key:

{{ products[random(5)] }}

Tip

The [] is used if you want force getting the attribute off of an object like an array, instead of trying to access the property. That’s a very rare case, so don’t worry about it.

Getting Data from an Object

I’m going to complicate things again by changing what the products variable looks like. But first, use our friend the dump function to see that products is just a collection of strings right now:

{{ dump(products) }}

Now, I’ll change the products variable:

// index.php
// ...

echo $twig->render('homepage.twig', array(
    // ...
    'products' => array(
        new Product('Serious Businessman', 'formal.png'),
        new Product('Penguin Dress', 'dress.png'),
        new Product('Sportstar Penguin', 'sports.png'),
        new Product('Angel Costume', 'angel-costume.png'),
        new Product('Penguin Accessories', 'swatter.png'),
        new Product('Super Cool Penguin', 'super-cool.png'),
    ),
));

After my change, refresh the page to see that products is now a collection of Product objects. Each Product object has a name and imagePath property.

If we don’t change anything inside Twig, we’ll get an error:

Catchable fatal error: Object of class Product could not be converted to string in twig/vendor/twig/twig/lib/Twig/Environment.php(320) : eval()’d code on line 30

This means that we can print a string, but not an object. That makes sense. Each Product object has name and imagePath properties, and we really want to print those individually.

Tip

If an object has a __toString method, then it actually can be printed.

And guess what?! We can use the period character once again to do this! Even though pageData is an array and each product is an object, getting data off each is exactly the same:

{% for product in products %}
    <div class="span4">
        <h2>{{ product.name }}</h2>
        <div class="product-img">
            <img src="assets/images/{{ product.imagePath }}" class="img-rounded" />
        </div>
    </div>
{% endfor %}

Refresh the page to see that our products have more details!

Tip

In your project, you’ll likely have a Twig function or variable that you use when referring to static images, CSS or JS files. Check your documentation to see.

Alright! By using the dump function, we can see what a variable looks like. We can print it, loop over it, or print a child key or property for it. We’re dangerous like a killer whale!

For the more technical folk, behind the scenes, Twig checks to see if the Product class has a public name property. If the property doesn’t exist or isn’t public, it looks for a getName method and calls it to get the value. This lets us say product.name without really caring how the PHP code for the class looks.

Tip

You can also call a method on an object if you need to:

{{ product.getName() }}

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