Enums (PHP 8.1)

Part of the Object Oriented Programming section of Coddy's PHP journey. Lesson 59 of 91.

Before PHP 8.1, representing a fixed set of values like statuses or types meant using class constants or magic strings - both error-prone approaches. Enums (enumerations) provide a proper way to define a type that can only hold specific, predefined values.

Define an enum using the enum keyword:

<?php
enum Status {
    case Pending;
    case Active;
    case Completed;
}

$status = Status::Active;
echo $status->name;

Output:

Active

Enums can also have backed values - string or integer values associated with each case. This is useful when storing enums in databases or APIs:

<?php
enum Status: string {
    case Pending = 'pending';
    case Active = 'active';
    case Completed = 'completed';
}

$status = Status::Active;
echo $status->value;

Output:

active

Backed enums provide a from() method to create an enum from its value, and tryFrom() which returns null instead of throwing an error for invalid values:

<?php
$status = Status::from('active');      // Returns Status::Active
$invalid = Status::tryFrom('unknown'); // Returns null

Enums can also contain methods, making them powerful for encapsulating related logic. They work seamlessly with type hints, ensuring your functions only accept valid values - no more checking if a string matches expected options.

Challenge

Easy

Let's build an order management system that uses enums to represent order statuses in a type-safe way. Instead of relying on strings that could be misspelled or invalid, you'll create a backed enum that maps each status to a database-friendly value.

You'll organize your code across three files:

OrderStatus.php: Create a string-backed enum called OrderStatus with four cases:
- Pending backed by 'pending'
- Processing backed by 'processing'
- Shipped backed by 'shipped'
- Delivered backed by 'delivered'
Add a method label() that returns a human-readable description for each status:
- Pending returns "Awaiting confirmation"
- Processing returns "Being prepared"
- Shipped returns "On the way"
- Delivered returns "Order complete"
Order.php: Create an Order class that uses the enum. Include the OrderStatus file. The class should:
- Accept an order ID (string) and an OrderStatus in its constructor using constructor promotion
- Have a method getInfo() that returns "Order [id]: [status label]"
- Have a method getStatusValue() that returns the backed value of the status (useful for database storage)
main.php: Include the Order file. You'll receive two inputs: an order ID and a status string (like "shipped"). Use tryFrom() to safely convert the string input to an OrderStatus enum. If the status is valid, create an Order and print two lines:
- The result of getInfo()
- The result of getStatusValue()
If the status string is invalid, print "Invalid status".

This challenge demonstrates how enums provide type safety. Your Order class can only accept valid statuses, and the tryFrom() method lets you safely handle user input without risking invalid values.

Try it yourself

<?php

require_once 'Order.php';

// Read input
$orderId = trim(fgets(STDIN));
$statusString = trim(fgets(STDIN));

// TODO: Use OrderStatus::tryFrom() to safely convert the status string to an enum
// tryFrom() returns null if the value is invalid

// TODO: If the status is valid, create an Order and print:
// - The result of getInfo()
// - The result of getStatusValue()

// TODO: If the status is invalid, print "Invalid status"

?>

Test yourself

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