Intersection types in practice in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an intersection type in PHP?

An intersection type requires a value to satisfy multiple type constraints at the same time. It means the value must be an instance of all specified types.

beginner

How do you declare an intersection type in PHP 8.1+?

You use the ampersand (&) symbol between types, for example: <code>function example(SomeInterface&AnotherInterface $obj) {}</code> means $obj must implement both interfaces.

intermediate

Why use intersection types in practice?

They help ensure that a value meets multiple requirements, improving code safety and clarity by enforcing multiple behaviors or properties at once.

intermediate

Can intersection types be used with classes and interfaces together?

Yes. For example, ClassA&InterfaceB means the value must be an instance of ClassA and also implement InterfaceB.

beginner

What happens if a value does not satisfy all types in an intersection type declaration?

PHP will throw a TypeError at runtime, indicating the value does not meet the required intersection type constraints.

Which symbol is used to declare intersection types in PHP?

A ,

B |

C &

D :

The ampersand (&) symbol is used to declare intersection types, meaning the value must satisfy all listed types.

What does the intersection type A&B mean in PHP?

A Value must be both A and B

B Value must be A but not B

C Value must be neither A nor B

D Value must be either A or B

Intersection types require the value to satisfy all types, so it must be both A and B.

Can intersection types include multiple interfaces?

A Only traits can be combined

B No, only classes

C Only one interface is allowed

D Yes, multiple interfaces can be combined

Multiple interfaces can be combined using intersection types to require a value to implement all of them.

What error occurs if a value does not meet an intersection type requirement?

A ParseError

B TypeError

C Warning

D Notice

PHP throws a TypeError when a value does not satisfy the intersection type constraints.

Which PHP version introduced intersection types?

A PHP 8.1

B PHP 8.0

C PHP 7.4

D PHP 8.2

Intersection types were introduced in PHP 8.1.

Explain how intersection types improve code safety in PHP.

Think about how requiring multiple interfaces or classes helps avoid wrong values.

Describe how to declare and use an intersection type with a class and an interface in PHP.

Show a function parameter that requires an object to be both a class instance and implement an interface.