Enums in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an enum in PHP?

An enum in PHP is a special type that lets you define a set of named values. It helps group related constants together, making code easier to read and safer.

beginner

How do you define a basic enum in PHP?

Use the enum keyword followed by the enum name and a list of cases inside curly braces. For example:

enum Status { case Pending; case Approved; case Rejected; }

intermediate

What is a backed enum in PHP?

A backed enum associates each case with a scalar value like a string or int. This lets you store or compare enum cases easily. Example:

enum Status: string { case Pending = 'pending'; case Approved = 'approved'; }

intermediate

How do you get the scalar value of a backed enum case?

You access the value property of the enum case. For example:

$status = Status::Pending; echo $status->value; // outputs 'pending'

advanced

Can enums in PHP have methods?

Yes! Enums can have methods just like classes. This lets you add behavior related to the enum cases. For example:<br><pre>enum Status { case Pending; case Approved; function label() { return match($this) { self::Pending => 'Waiting', self::Approved => 'Done' }; } }</pre>

Which keyword is used to define an enum in PHP?

A enum

B class

C interface

D const

The enum keyword is used to define enums in PHP.

What type of values can backed enums have in PHP?

A Only strings

B Only integers

C Any data type

D Strings or integers

Backed enums in PHP can have either string or integer scalar values.

How do you access the scalar value of a backed enum case?

A Using the <code>name</code> property

B Using the <code>value</code> property

C Using the <code>getValue()</code> method

D Using the <code>toString()</code> method

The scalar value of a backed enum case is accessed via the value property.

Can PHP enums have methods?

A Only static methods are allowed

B No, enums cannot have methods

C Yes, enums can have methods

D Only abstract methods are allowed

PHP enums can have methods to add behavior related to the enum cases.

Which PHP version introduced enums?

A PHP 8.1

B PHP 7.4

C PHP 8.0

D PHP 8.2

Enums were introduced in PHP 8.1.

Explain what enums are in PHP and why they are useful.

Think about how enums help organize fixed sets of values.

Describe the difference between pure enums and backed enums in PHP.

Consider how backed enums store extra information.

Practice

1. What is the main purpose of using enum in PHP?

easy

A. To group related constant values under one name

B. To create a new type of variable that can hold any value

C. To define functions inside classes

D. To declare variables with dynamic types

Solution

1. Step 1: Understand what enums represent

   Enums are used to group related constant values, like fixed options or states.

2. Step 2: Compare with other options

   Other options describe unrelated concepts: variables or functions, not enums.

3. Final Answer:

   To group related constant values under one name -> Option A

4. Quick Check:

   Enums = group constants [OK]

Hint: Enums group fixed options clearly [OK]

Common Mistakes:

• Thinking enums create dynamic variables
• Confusing enums with classes or functions
• Assuming enums can hold any value

2. Which of the following is the correct syntax to declare a backed enum with string values in PHP?

easy

A. enum Status: string { case Active = 'active'; case Inactive = 'inactive'; }

B. enum Status { case Active = 'active'; case Inactive = 'inactive'; }

C. enum Status: int { case Active = 'active'; case Inactive = 'inactive'; }

D. enum Status: string { Active = 'active'; Inactive = 'inactive'; }

Solution

1. Step 1: Identify backed enum syntax

   Backed enums require a type after the enum name, like : string, and cases with assigned values.

2. Step 2: Check each option

   enum Status: string { case Active = 'active'; case Inactive = 'inactive'; } correctly uses enum Status: string { case Active = 'active'; ... }. enum Status { case Active = 'active'; case Inactive = 'inactive'; } misses the type. enum Status: int { case Active = 'active'; case Inactive = 'inactive'; } uses wrong type int with string values. enum Status: string { Active = 'active'; Inactive = 'inactive'; } misses case keyword.

3. Final Answer:

   enum Status: string { case Active = 'active'; case Inactive = 'inactive'; } -> Option A

4. Quick Check:

   Backed enum syntax = enum Status: string { case Active = 'active'; case Inactive = 'inactive'; } [OK]

Hint: Backed enums need type and 'case' keyword [OK]

Common Mistakes:

• Omitting the enum type after colon
• Forgetting 'case' before each value
• Assigning string values to int enums

3. What will be the output of the following PHP code?

enum Direction { case North; case South; case East; case West; }
$dir = Direction::East;
echo $dir->name;

medium

A. Error: Cannot access name

B. direction::East

C. East case

D. East

Solution

1. Step 1: Understand enum case name property

   In PHP enums, $dir->name returns the case name as a string.

2. Step 2: Check the assigned case

   The variable $dir is assigned Direction::East, so $dir->name is "East".

3. Final Answer:

   East -> Option D

4. Quick Check:

   Enum case name = East [OK]

Hint: Use ->name to get enum case name string [OK]

Common Mistakes:

• Expecting the value instead of name
• Trying to print enum case directly
• Confusing case name with enum class name

4. Identify the error in this PHP enum declaration:

enum Color {
  case Red = 1;
  case Green = 2;
  case Blue;
}

medium

A. Case Blue should have a value assigned

B. Missing enum type for backed enum values

C. Enum name must be lowercase

D. Cases cannot have integer values

Solution

1. Step 1: Check enum type for backed values

   When enum cases have assigned values (like 1, 2), the enum must declare a type (e.g., : int).

2. Step 2: Analyze the given enum

   The enum Color assigns values to some cases but does not specify : int after the enum name, causing a syntax error.

3. Final Answer:

   Missing enum type for backed enum values -> Option B

4. Quick Check:

   Backed enums need type declared [OK]

Hint: Backed enums must declare type after enum name [OK]

Common Mistakes:

• Not declaring enum type when assigning values
• Assuming cases can mix assigned and unassigned values
• Thinking enum names must be lowercase

5. Given this enum:

enum Status: string {
  case Pending = 'pending';
  case Approved = 'approved';
  case Rejected = 'rejected';
}

Which code correctly converts a string $input to the matching Status enum case or returns null if no match?

hard

A. new Status($input)

B. Status::from($input)

C. Status::tryFrom($input)

D. Status::$input

Solution

1. Step 1: Understand enum methods for backed enums

   PHP backed enums provide from() which throws error if no match, and tryFrom() which returns null if no match.

2. Step 2: Match requirement

   The question asks to return matching enum or null if no match, so tryFrom() is correct.

3. Final Answer:

   Status::tryFrom($input) -> Option C

4. Quick Check:

   Safe enum conversion = tryFrom() [OK]

Hint: Use tryFrom() to safely convert string to enum [OK]

Common Mistakes:

• Using from() which throws error on no match
• Trying to instantiate enum with new
• Accessing enum cases as static properties