PHP __invoke
__invoke() magic method and how to use it effectively.Introduction to the PHP __invoke() magic method
Suppose that you have a class called MyClass:
class MyClass
{
// ...
}Code language: PHP (php)
Typically, you create a new instance of the MyClass and access its methods and properties like this:
$instance = new MyClass();
$instance->methodName();Code language: PHP (php)
Or if the MyClass has static methods, you can access them using the :: operator:
MyClass::staticMethod();Code language: PHP (php)
Besides using the MyClass these ways, PHP allows you to use the object of the class as a function. For example:
$instance($arguments);Code language: PHP (php)
In this case, PHP will call the __invoke() method of the MyClass. For example:
class MyClass
{
public function __invoke(...$arguments)
{
echo 'Called to the __invoke method';
}
}
$instance = new MyClass;
$instance();
Code language: PHP (php)
Output:
Called to the __invoke methodCode language: PHP (php)
The $instance is known as a function object or functor.
The __invoke() magic method has the following syntax:
__invoke( ...$values): mixedCode language: PHP (php)
PHP will call the __invoke() magic method when you call an object as a function.
Also, the object of the class that implements the __invoke() magic method is a callable. For example:
echo is_callable($instance) ? 'yes' : 'no'; // yesCode language: PHP (php)
In this example, the $instance of the MyClass is a callable. This means that you can pass it to any function or method that accepts a callable.
Practical PHP __invoke() magic method example
Suppose that you have an array of customer data like this;
$customers = [
['id' => 1, 'name' => 'John', 'credit' => 20000],
['id' => 3, 'name' => 'Alice', 'credit' => 10000],
['id' => 2, 'name' => 'Bob', 'credit' => 15000]
];Code language: PHP (php)
To sort the customers by name or credit, you can use the usort() function. The second parameter of the usort() function is a callable that determines the sort order:
usort(array &$array, callable $callback): bool
Code language: PHP (php)
The following defines the class Comparator that implements the __invoke() magic method:
class Comparator
{
private $key;
public function __construct(string $key)
{
$this->key = $key;
}
public function __invoke($a, $b)
{
return $a[$this->key] <=> $b[$this->key];
}
}
Code language: PHP (php)
The __invoke() method returns the result of the comparison of two array elements by a specified key.
To use the Comparator class, you can create a new instance of the class and pass it to the usort() function as follows:
usort($customers, new Comparator('name'));Code language: PHP (php)
This statement sorts the customers by name.
To sort the customers by credit, you can use the credit as the key like this:
usort($customers, new Comparator('credit'));Code language: PHP (php)
Put it all together.
class Comparator
{
private $key;
public function __construct(string $key)
{
$this->key = $key;
}
public function __invoke($a, $b)
{
return $a[$this->key] <=> $b[$this->key];
}
}
$customers = [
['id' => 1, 'name' => 'John', 'credit' => 20000],
['id' => 3, 'name' => 'Alice', 'credit' => 10000],
['id' => 2, 'name' => 'Bob', 'credit' => 15000]
];
// sort customers by names
usort($customers, new Comparator('name'));
print_r($customers);
// sort customers by credit
usort($customers, new Comparator('credit'));
print_r($customers);
Code language: PHP (php)
Summary
- Use the
__invoke()magic method is invoked when you call an object as a function. - An object of a class that implements the
__invoke()is known as a function object or functor. It’s also a callable.