Prior to PHP 7, there was no need to declare the data type of the arguments passed to a function or class method. Also, there was no need to mention the return data type. Any data type can be passed to and returned from a function or method. This is one of the huge problems in PHP, in which it is not always clear which data types should be passed or received from a function or method. To fix this problem, PHP 7 introduced type hints. As of now, two type hints are introduced: scalar and return type hints. These are discussed in the following sections.

Type hints is a feature in both OOP and procedural PHP because it can be used for both procedural functions and object methods.

class Person
{
  public function age(int $age)
  {
    return $age;
    }

  public function name(string $name)
  {
    return $name;
    }

  public function isAlive(bool $alive)
  {
    return $alive;
    }

}

$person = new Person();
echo $person->name('Altaf Hussain');
echo $person->age(30);
echo $person->isAlive(TRUE);

echo $person->age(30.5);

declare(strict_types = 1);

echo $person->isAlive('true');

class Person
{
  public function age(float $age) : string
  {
    return 'Age is '.$age;
  }

  public function name(string $name) : string
  {
    return $name;
    }

  public function isAlive(bool $alive) : string
  {
    return ($alive) ? 'Yes' : 'No';
  }

}

class Address 
{
  public function getAddress()
  {
  return ['street' => 'Street 1', 'country' => 'Pak'];
  }
}

class Person
{
  public function age(float $age) : string
  {
    return 'Age is '.$age;
  }

  public function name(string $name) : string
  {
    return $name;
  }

  public function isAlive(bool $alive) : string
  {
    return ($alive) ? 'Yes' : 'No';
  }

  public function getAddress() : Address
  {
  return new Address();
  }
}

public function getAddress() : Address
{
  return ['street' => 'Street 1', 'country' => 'Pak'];
}

Fatal error: Uncaught TypeError: Return value of Person::getAddress() must be an instance of Address, array returned

In a very large codebase, classes are divided into namespaces, which makes them easy to manage and work with. However, if there are too many classes in a namespace and we need to use 10 of them, then we have to type the complete use statement for all these classes.

For example, we have a Publishers/Packt namespace and the classes Book, Ebook, Video, and Presentation. Also, we have a functions.php file, which has our normal functions and is in the same Publishers/Packt namespace. Another file, constants.php, has the constant values required for the application and is in the same namespace. The code for each class and the functions.php and constants.php files is as follows:

//book.php
namespace Publishers\Packt;

class Book 
{
  public function get() : string
  {
    return get_class();
  }
}

Now, the code for the Ebook class is as follows:

//ebook.php
namespace Publishers\Packt;

class Ebook 
{
  public function get() : string
  {
    return get_class();
  }
}

The code for the Video class is as follows:

//presentation.php
namespace Publishers\Packt;

class Video 
{
  public function get() : string
  {
    return get_class();
  }
}

Similarly, the code for the presentation class is as follows:

//presentation.php
namespace Publishers\Packt;

class Presentation 
{
  public function get() : string
  {
    return get_class();
  }
}

All the four classes have the same methods, which return the classes' names using the PHP built-in get_class() function.

Now, add the following two functions to the functions.php file:

//functions.php

namespace Publishers\Packt;

function getBook() : string
{
  return 'PHP 7';
}
function saveBook(string $book) : string
{
  return $book.' is saved';
}

Now, let's add the following code to the constants.php file:

//constants.php
  
namespace Publishers/Packt;

const COUNT = 10;
const KEY = '123DGHtiop09847';
const URL = 'https://www.Packtpub.com/';

The code in both functions.php and constants.php is self-explanatory. Note that each file has a namespace Publishers/Packt line at the top, which makes these classes, functions, and constants belong to this namespace.

Now, there are three ways to use the classes, functions, and constants. Let's consider each one.

Take a look at the following code:

//Instantiate objects for each class in namespace

$book = new Publishers\Packt\Book();
$ebook = new Publishers\Packt\Ebook();
$video = new Publishers\Packt\Video();
$presentation = new Publishers\Packt\Presentation();

//Use functions in namespace

echo Publishers/Packt/getBook();
echo Publishers/Packt/saveBook('PHP 7 High Performance');

//Use constants

echo Publishers\Packt\COUNT;
echo Publishers\Packt\KEY;

In the preceding code, we used namespace names directly while creating objects or using functions and constants. The code looks fine, but it is cluttered. Namespace is everywhere, and if we have lots of namespaces, it will look very ugly, and the readability will be affected.

Now, let's rewrite the preceding code to make it more readable, as follows:

use Publishers\Packt\Book;
use Publishers\Packt\Ebook;
use Publishers\Packt\Video;
use Publishers\Packt\Presentation;
use function Publishers\Packt\getBook;
use function Publishers\Packt\saveBook;
use const Publishers\Packt\COUNT;
use const Publishers\Packt\KEY;

$book = new Book();
$ebook = new Ebook(();
$video = new Video();
$pres = new Presentation();

echo getBook();
echo saveBook('PHP 7 High Performance');

echo COUNT; 
echo KEY;

In the preceding code, at the top, we used PHP statements for specific classes, functions, and constants in a namespace. However, we still wrote duplicate lines of code for each class, function, and/or constant. This may lead to us have lots of use statements at the top of the file, and the overall verbosity would not be good.

To fix this problem, PHP 7 introduced group use declaration. There are three types of group use declarations:

use Publishers\Packt\{ Book, Ebook, Video, Presentation };
use function Publishers\Packt\{ getBook, saveBook };
use const Publishers\Packt\{ COUNT, KEY };

use Publishers\Packt\{ 
  Book,
  Ebook,
  Video,
  Presentation,
  function getBook,
  function saveBook,
  const COUNT,
  const KEY
};

use Publishers\Packt\Paper\Book;
use Publishers\Packt\Electronic\Ebook;
use Publishers\Packt\Media\{Video,Presentation};

use Publishers\Packt\{
  Paper\Book,
  Electronic\Ebook,
  Media\Video,
  Media\Presentation
};

An anonymous class is a class that is declared and instantiated at the same time. It does not have a name and can have the full features of a normal class. These classes are useful when a single one-time small task is required to be performed and there is no need to write a full-blown class for it.

The syntax of this class is the same as that of the named classes, but only the name of the class is missing, as shown in the following syntax:

new class(argument) { definition };

Let's look at a basic and very simple example of an anonymous class, as follows:

$name = new class() {
  public function __construct()
  {
    echo 'Altaf Hussain';
  }
};

The preceding code will just display the output as Altaf Hussain.

Arguments can also be passed to the anonymous class constructor, as shown in the following code:

$name = new class('Altaf Hussain') {
  public function __construct(string $name)
  {
    echo $name;
  }
};

This will give us the same output as the first example.

Anonymous classes can extend other classes and have the same parent-child classes functioning as normal named classes. Let's have another example; take a look at the following:

class Packt
{
  protected $number;
  
  public function __construct()
  {
    echo 'I am parent constructor';
  }

  public function getNumber() : float
  {
    return $this->number;
  }
}

$number = new class(5) extends packt
{
  public function __construct(float $number)
  {
    parent::__construct();
    $this->number = $number;
  }
};

echo $number->getNumber();

The preceding code will display I am parent constructor and 5. As can be seen, we extended the Packt class the way we extend named classes. Also, we can access the public and protected properties and methods within the anonymous class and public properties and methods using anonymous class objects.

Anonymous classes can implement interfaces too, the same as named classes. Let's create an interface first. Run the following:

interface Publishers
{
  public function __construct(string $name, string $address);
  public function getName();
  public function getAddress();
}

Now, let's modify our Packt class as follows. We added the highlighted code:

class Packt
{
  protected $number;
  protected $name;
  protected $address;
  public function …
}

The rest of the code is same as the first Packt class. Now, let's create our anonymous class, which will implement the Publishers interface created in the previous code and extend the new Packt class, as follows:

$info = new class('Altaf Hussain', 'Islamabad, Pakistan')extends packt implements Publishers
{
  public function __construct(string $name, string $address)
  {
    $this->name = $name;
    $this->address = $address;
  }

  public function getName() : string
  {
  return $this->name;
  }

  public function getAddress() : string
  {
  return $this->address;
  }
}

echo $info->getName(). ' '.$info->getAddress();

The preceding code is self-explanatory and will output Altaf Hussain along with the address.

It is possible to use anonymous classes within another class, as shown here:

class Math
{
  public $first_number = 10;
  public $second_number = 20;

  public function add() : float
  {
    return $this->first_number + $this->second_number;
  }

  public function multiply_sum()
  {
    return new class() extends Math
    {
      public function multiply(float $third_number) : float
      {
        return $this->add() * $third_number;
      }
    };
  }
}

$math = new Math();
echo $math->multiply_sum()->multiply(2);

The preceding code will return 60. How does this happen? The Math class has a multiply_sum method that returns the object of an anonymous class. This anonymous class is extended from the Math class and has a multiply method. So, our echo statement can be divided into two parts: the first is $math->multiply_sum(), which returns the object of the anonymous class, and the second is ->multiply(2), in which we chained this object to call the anonymous class's multiply method along with an argument of the value 2.

In the preceding case, the Math class can be called the outer class, and the anonymous class can be called the inner class. However, remember that it is not required for the inner class to extend the outer class. In the preceding example, we extended it just to ensure that the inner classes could have access to the outer classes' properties and methods by extending the outer classes.

Back in PHP 4, the constructor of a class has the same name method as that of the class. It is still used and is valid until PHP's 5.6 version. However, now, in PHP 7, it is deprecated. Let's have an example, as shown here:

class Packt
{
  public function packt()
  {
    echo 'I am an old style constructor';
  }
}

$packt = new Packt();

The preceding code will display the output I am an old style constructor with a deprecated message, as follows:

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; Packt has a deprecated constructor in…

However, the old style constructor is still called. Now, let's add the PHP __construct method to our class, as follows:

class Packt
{
  public function __construct()
  {
    echo 'I am default constructor';
  }

  public function packt()
  {
    echo 'I am just a normal class method';
  }
}

$packt = new Packt();
$packt->packt();

In the preceding code, when we instantiated the object of the class, the normal __construct constructor was called. The packt()method isn't considered a normal class method.

PHP 7 introduced a base interface that can be base for every object that can use the throw statement. In PHP, exceptions and errors can occur. Previously, exceptions could be handled, but it was not possible to handle errors, and thus, any fatal error caused the complete application or a part of the application to halt. To make errors (the most fatal errors) catchable as well, PHP 7 introduced the throwable interface, which is implemented by both the exception and error.

We all know exceptions, so in this topic, we will only discuss errors, which can handle the ugly, fatal errors.

function iHaveError($object)
{
  return $object->iDontExist();
  {

//Call the function
iHaveError(null);
echo "I am still running";

try 
{
  iHaveError(null);
} catch(Error $e)
{
  //Either display the error message or log the error message
  echo $e->getMessage();
}

echo 'I am still running';

try
{
  $a = 20;
  $division = $a / 20;
} catch(DivisionByZeroError $e) 
{
  echo $e->getMessage();
}