PHP type hinting is something I’m a huge fan of and think everyone should use. It removes a lot of the guesswork from your PHP; you know that your method will only accept certain types. Being able to know this in advance will help reduce unexpected errors.

PHP’s Basic Types

Scalar Types

A scalar type holds a single value.

  • bool
  • int
  • float
  • string

Compound Types

A compound type may contain multiple values. Below are the compound types that PHP supports.

  • array
  • callable
  • class/interface name

Example of Scalar/Compound Types

Below is an example of type hinting your methods; I’ve added comments to help explain.

Type hinting keeps you from having to use functions like is_int to ensure your method is receiving the correct type.

PHP Object Oriented Types

When you’re learning to write object oriented PHP, it can be a bit difficult to grasp the concept and understand the benefits. I encourage you to write/use classes whenever you can, instead of using procedural code. If you keep practicing, you’ll get better, and eventually become a more efficient developer. Below is an example of using a concrete class as a type hint.

Type Hint with Concrete Class

Our Weight class expects an integer since lbs is a standard measurement. The RowingMachine class expects a string since I have no idea what kind of settings one may have.

The Exercise class has two methods, lift() and row(). Unless you’re really strong, I don’t think you want to lift the rowing machine, so lift() only accepts the type Weight. If lift() accepted the interface GymEquipment then it could accept a RowingMachine as an argument. The row() method of the Exercise class only accepts a type of RowingMachine.

Type Hint with Interface

Let’s see how we would type hint using an interface. We will need to refactor our code a little bit, and it will usually benefit us by doing this.

By using an interface as a type hint, we can pass multiple concrete classes as a parameter, as long as the class implements the interface. By doing this, you aren’t restricting yourself.


If you would like to practice object-oriented PHP on your own, try writing the Exercise example that also accepts a name. Then, when it echo’s out the action, have it include a name from the Exercise construct. If you want to write something else, then do that, do what interests you. Put your code on GitHub and email it to me; also email me if you have any questions.