Enums

Learn to define and use type-safe constants with enum.

Type-safe constants with enum

PHP 8.1 introduced enum to define a fixed set of values in a type-safe way. A Suit enum can list card suit names; it makes invalid values impossible.

Each case represents one value and stands for a singleton instance. Suit::Heart always returns the same object.

A parameter typed as Suit accepts only the four valid values; anything else fails at compile time or runtime.

Backed enum and enum methods

An enum can carry an int or string backed value: enum Status: int { case Active = 1; }. The int here is a scalar type; with PHP 8.0 union types parameters can also take combined types like int|string.

Backed enums expose Status::Active->value to read the value and Status::from(1) to build a case from a value.

An enum can also hold methods; a match expression inside picks behavior per case, so logic stays bound to state.

Exercise Suit backed enum

Define a string backed enum called Suit. Cases: Heart = "H", Diamond = "D", Club = "C", Spade = "S".

The echo line below should print H.

Show example solution

enum Suit: string {
  case Heart = "H";
  case Diamond = "D";
  case Club = "C";
  case Spade = "S";
}

echo Suit::Heart->value;

Test yourself

Complete the enum case

enum Suit {
  case Heart;
  case Diamond;
  case ____;
  case Spade;
}

Show answer

enum Suit {
  case Heart;
  case Diamond;
  case Club;
  case Spade;
}

What does Status::Active->value return?
```
enum Status: int {
  case Active = 1;
  case Paused = 2;
}
```
- Active
- 1
- Status
- true
Show answer

1 — Correct. Since the Active case is backed by 1, ->value returns 1.
Match the enum concepts

enum

typed constant set
case

enum member
backed

value-carrying enum
->value

access backed value

Next lesson: The match expression

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