Traversing an associative arrays

The foreach loop construct is ideal for iterating over an associative array; when a foreach loop is used, both the key and the value will be made available as variables.

First, this is how to iterate over a single-dimensional array:

foreach ($teachers as $teacher => $email) {
  echo PHP_EOL . $teacher . ':' . $email;
}

Output:

Rasmus Lerdorf:[email protected]
Zeev Suraski:[email protected]
Andi Gutmans:[email protected]

To iterate over multi-dimensional arrays can be a challenge, especially if we do not know the level of nesting the array is going to have. However, for a simple two-dimensional array like the one used in this tutorial, you could just "hard-code" the code that deals with the second-level arrays:

foreach ($teachers as $teacher => $data) {
    echo PHP_EOL . $teacher . PHP_EOL .
        ' E-mail: ' . $data['e-mail'] . PHP_EOL .
        ' Born: ' . $data['born'];
}

Output:

Rasmus Lerdorf
 E-mail: [email protected]
 Born: 1968
Zeev Suraski
 E-mail: [email protected]
 Born: 1976
Andi Gutmans
 E-mail: [email protected]
 Born: 1972

Objects vs arrays

When you are working with object orientated PHP, it is often better to use objects instead of arrays; this is because of benefits such as security added from type hinting and auto completion in your code editor.

Objects can also be iterated over using a foreach loop, so they are almost functionally identical when only used with properties.

If you were to remake the $teachers array from earlier, then you could do it like so:

$teachers = new teachers();

$teachers->{'Rasmus Lerdorf'} = '[email protected]';
$teachers->{'Zeev Suraski'} = '[email protected]';
$teachers->{'Andi Gutmans'} = '[email protected]';

foreach ($teachers as $name => $email) {
  echo $name . ": ", $email . '<br>';
}

This example uses complex syntax to create the property names, since normally you would not be able to include spaces in property names; by using the complex curly syntax, we can use any character as the property name, similarly to how we may use any character as a key value in an array.

Auto completion

The above example is not very good, since it might break auto completion because of the use of complex syntax. Instead, you should consider the below example:

class student {

   public $name;
   public $age;

   public function __construct(string $name, int $age)
   {
     $this->age = $age;
     $this->name = $name;
   }
}

$some_student = new student('Jacob', 20);

echo $some_student->name;

This allows you to leverage auto-completion in an editor like Visual Studio Code with PHP Intelephense:

To iterate over the object, you can still use a foreach loop:

foreach ($some_student as $key => $value) {
  echo $key . ": ", $value . '<br>';
}

class student
{

  public $name;
  public $age;

  public function __construct(string $name, int $age)
  {
    $this->age = $age;
    $this->name = $name;
  }
}

class teacher
{

  private $student;

  public function __construct(student $student)
  {
    $this->student = $student;

    echo '<p>The name of the student I am teaching today is: </p>';
    echo "<p><b>{$this->student->name}</b></p>";
    exit();
  }
}