Pure Intersection Types in PHP 8.1

Pure intersection types are a new feature introduced in PHP 8.1. While union types accept a value that matches any one of the listed types, intersection types require the value to satisfy all specified types simultaneously.

This is especially useful when a function needs to work with objects that implement several interfaces. For example, the following function accepts a parameter that implements both HasTitle and HasId interfaces, allowing it to generate a slug from the title and identifier:

function generateSlug(HasTitle&HasId $post) {
    return strtolower($post->getTitle()) . $post->getId();
}

Without intersection types, developers would have to create a new interface (e.g., Sluggable) that extends the required interfaces, adding extra boilerplate. Intersection types eliminate this overhead.

For the full specification, see the RFC: https://wiki.php.net/rfc/pure-intersection-types .

Related articles that explore other PHP 8.1 features include:

PHP 8.1 Enums

PHP 8.1 Readonly Properties

PHP 8.1 Initializers

PHP 8.1 Fibers

PHP 8.1 Array Unpacking with String Keys