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PHP: How to declare the expected type for an array to pass to an abstract method

PHP arrays may host mixed content. The language processor won't complain if you write this:

$list = [
  'some-string',
  3,
  [ 'key' => 'value' ]
];

That can be useful in many cases but what if you want to declare an abstract method and indicate to developers what it should get?

abstract class MyClass {
  public abstract function my_function($args);
}

First approach: make the developer aware of the type #

Adding a comment is enough to tell the developers what your method expect:

abstract class MyClass {
  /**
   * This method will process a list of objects.
   *
   * @param MyObjects[] $args
   */
    public abstract static function my_function($args);
}

Second approach: make PHP aware of the type #

Declaring the argumens as an array is not enough, as it won't indicate the type of what should be inside the array:

public abstract static function my_function(array $args);

We'll have to transform the array argument into a variable list of MyObject arguments:

public abstract static function my_function(MyObject ...$args);

On the caller side, the syntax will need to be changed to spread the arrray:

$result = MyClass::my_function(...$array_of_objects);

Final thoughts #

Both approaches can (and should) be mixed: add comments for the developers & make PHP aware of the type.

This implementation makes it easier to follow the types of the variables that are passed across the code but it has a drawback. By declaring a variable list of arguments to a method, you won't be able to pass multiple lists of different types to it.

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