Using static properties and methods

PHP lets you access properties or methods without having to create an instance of the class. The keyword used for this purpose is static.

How to do it...

At its simplest, simply add the static keyword after stating the visibility level when declaring an ordinary property or method. Use the self keyword to reference the property internally:
```
class Test
{
  public static $test = 'TEST';
  public static function getTest()
  {
    return self::$test;
  }
}
```
The self keyword will bind early, which will cause problems when accessing static information in child classes. If you absolutely need to access information from the child class, use the static keyword in place of self. This process is referred to as Late Static Binding.
In the following example, if you echo Child::getEarlyTest(), the output will be TEST. If, on the other hand, you run Child::getLateTest(), the output will be CHILD. The reason is that PHP will bind to the earliest definition when using self, whereas the latest binding is used for the static keyword:
```
class Test2
{
  public static $test = 'TEST2';
  public static function getEarlyTest()
  {
    return self::$test;
  }
  public static function getLateTest()
  {
    return static::$test;
  }
}

class Child extends Test2
{
  public static $test = 'CHILD';
}
```

In many cases, the Factory design pattern is used in conjunction with static methods to produce instances of objects given different parameters. In this example, a static method factory() is defined which returns a PDO connection:

public static function factory(
  $driver,$dbname,$host,$user,$pwd,array $options = [])
  {
    $dsn = sprintf('%s:dbname=%s;host=%s', 
    $driver, $dbname, $host);
    try {
        return new PDO($dsn, $user, $pwd, $options);
    } catch (PDOException $e) {
        error_log($e->getMessage);
    }
  }

How it works...

You can reference static properties and methods using the class resolution operator "::". Given the Test class shown previously, if you run this code:

echo Test::$test;
echo PHP_EOL;
echo Test::getTest();
echo PHP_EOL;

You will see this output:

To illustrate Late Static Binding, based on the classes Test2 and Child shown previously, try this code:

echo Test2::$test;
echo Child::$test;
echo Child::getEarlyTest();
echo Child::getLateTest();

The output illustrates the difference between self and static:

Finally, to test the factory() method shown previously, save the code into the Application\Database\Connection class in a Connection.php file in the Application\Database folder. You can then try this:

include __DIR__ . '/../Application/Database/Connection.php';
use Application\Database\Connection;
$connection = Connection::factory(
'mysql', 'php7cookbook', 'localhost', 'test', 'password');
$stmt = $connection->query('SELECT name FROM iso_country_codes');
while ($country = $stmt->fetch(PDO::FETCH_COLUMN)) 
echo $country . '';

You will see a list of countries pulled from the sample database:

Table of Contents for
PHP 7: Real World Application Development

Using static properties and methods

How to do it...

How it works...

See also

Table of Contents for PHP 7: Real World Application Development

Using static properties and methods

How to do it...

How it works...

See also

Table of Contents for
PHP 7: Real World Application Development