Enums in PHP

Learn to define pure enums and backed enums (string/int) in PHP 8.1, use enum methods, implement interfaces, and apply enums in real scenarios.

Introduction to Enums (PHP 8.1+)

Enums (PHP 8.1) are a first-class type that represents a fixed set of named values. They replace the common pattern of using class constants or integers to represent a finite set of options, with full type safety.

1. The Problem Enums Solve

Replace magic strings and integer constants with type-safe names.

Pure Enums

Pure enums (unit enums) have named cases with no associated value. They are used when you only need identity — not serialisation or database storage.

1. Defining & Using a Pure Enum

enum keyword with case declarations.

2. Comparing Enum Cases

Use === for identity comparison.

3. Enums in match Expressions

match is exhaustive and pairs perfectly with enums.

Backed Enums

Backed enums associate each case with a scalar value — useful for database storage, JSON serialisation, and API responses.

1. String-Backed Enum

Each case maps to a string value.

2. Integer-Backed Enum

Each case maps to an integer.

3. Listing All Cases — ::cases()

Get an array of all enum instances.

Enum Methods & Constants

Enums can contain methods and constants — making them richer than plain value holders.

1. Instance Methods

Add logic directly to the enum.

2. Static Methods & Constants

Factory helpers, utility logic, and shared constants.

Enums Implementing Interfaces

Enums can implement interfaces, enabling polymorphism and use in type-hinted parameters that accept any implementing type.

1. Implementing an Interface

Enums support implements but cannot extend classes.

Real-World Enum Patterns

Enums shine when replacing stringly-typed values, HTTP status codes, role systems, and state machines.

1. Database Storage

Store and retrieve enum values via their scalar backing.

2. HTTP Status Code Enum

Type-safe HTTP responses.