Using Enums to Model States

Enums represent a closed set of valid states instead of unvalidated strings.

The examples focus on the operation itself, including the important distinction: Free-form strings can contain invalid states; enum cases cannot.

What It Does

Use the examples below to observe the behavior on a small dataset before extending it to application code.

Before You Start

Read the input requirements before applying this pattern to production data.

Example 1: Basic Use

tryFrom returns null on unknown input, unlike from which throws ValueError.

<?php
enum TicketState: string { case New = "new"; case Ready = "ready"; case Done = "done"; }
$state = TicketState::tryFrom('new');
echo $state?->name ?? "invalid state";

Output from a successful local PHP 8.4 run:

New

Example 2: Checking Behavior

tryFrom returns null on unknown input, unlike from which throws ValueError.

<?php
enum TicketState: string { case New = "new"; case Ready = "ready"; case Done = "done"; }
$state = TicketState::tryFrom('ready');
echo $state?->name ?? "invalid state";

Output from a successful local PHP 8.4 run:

Ready

Example 3: Practical Example

tryFrom returns null on unknown input, unlike from which throws ValueError.

<?php
enum TicketState: string { case New = "new"; case Ready = "ready"; case Done = "done"; }
$state = TicketState::tryFrom('done');
echo $state?->name ?? "invalid state";

Output from a successful local PHP 8.4 run:

Done

Important Behavior and Edge Cases

Backed enums provide from/tryFrom for external scalar data, but adding a new case still requires consumers to handle it.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Enums represent a closed set of valid states instead of unvalidated strings.
• Backed enums provide from/tryFrom for external scalar data, but adding a new case still requires consumers to handle it.
• Free-form strings can contain invalid states; enum cases cannot.

Use Using Enums to Model States when its documented behavior matches the problem. Test the relevant edge cases in your own runtime before deploying it.