Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 31-45.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 31-45.


26 min read

Elevate your interview readiness with advanced PHP insights. From closures and late static binding to design patterns, Dependency Injection, and PHP 8 features, this segment (Questions 31-45) equips you for technical interview success.

31. What is a closure in PHP? Provide an example.

A closure, also known as an anonymous function or lambda function, is a self-contained block of code that can be defined without a formal function name. Closures are a powerful feature in PHP that allows you to create functions on-the-fly, often used for short and specific tasks. They can capture and use variables from their surrounding scope, even after the scope has exited.

Example of a Closure:

$multiplier = 3;

$timesTo = function($x) use ($multiplier) {
    return $x * $multiplier;

$result = $timesTo(5); // Result: 15

Use Cases for Closures:

  1. Callbacks: Closures can be passed as callbacks to functions like array_map, array_filter, and usort.

  2. Event Handling: Closures can be used to define event handlers in GUI frameworks and asynchronous programming.

  3. Factory Functions: Closures can be used to create factory functions that generate different types of objects.

  4. Data Transformation: Closures can be used to transform data in a flexible and reusable manner.

Example of Using a Closure as a Callback:

$numbers = [1, 2, 3, 4, 5];
$incremented = array_map(function($n) { return $n + 1; }, $numbers);
// Result: [2, 3, 4, 5, 6]

32. What is the difference between closures in PHP and JavaScript?

Closures in PHP vs JavaScript:

Closures in both PHP and JavaScript are similar in concept as they both allow you to define anonymous functions that can capture variables from their surrounding scopes. However, there are some differences in their usage and behavior:

  1. Lexical Scoping:

    • PHP: Closures in PHP have access to variables from their surrounding scope using the use keyword. However, they don't have "lexical scoping," meaning they can't modify the variables of the surrounding scope.

    • JavaScript: Closures in JavaScript have access to variables from their surrounding scope, and they exhibit "lexical scoping," which means they can modify those variables(declared by let).

  2. this Keyword:

    • PHP: Closures in PHP don't capture the $this object by default. If you want to access the current object within a closure, you need to explicitly bind it using the use keyword.

    • JavaScript: In JavaScript, closures capture the this object by default, allowing you to access the context in which the closure was defined.

  3. Syntax:

    • PHP: Closures are defined using the function keyword or the shorter arrow syntax fn().

    • JavaScript: Closures are defined using the function keyword or the arrow function syntax () => {}.

  4. Usage:

    • PHP: Closures are often used as callbacks for array functions, event handlers, and encapsulating logic.

    • JavaScript: Closures are extensively used for callbacks, promises, asynchronous programming, and more.

  5. Creating Closures in PHP and JavaScript:

    • In PHP, closures are often created using anonymous functions, although named functions can be used as well. Anonymous functions are commonly used to create closures due to their convenience.

    • In JavaScript, closures can be created using both named and anonymous functions. This flexibility allows for various use cases, such as callbacks, event handling, and private data encapsulation.

  6. Creating Private Variables and Methods:

    • In JavaScript, closures can be used to create private variables and methods. This is achieved by defining variables and functions within a closure's scope, making them inaccessible from outside the closure.

    • In PHP, closures don't inherently provide the same level of encapsulation for creating private variables and methods. While you can use anonymous functions to create closures, access control mechanisms for encapsulation are typically managed through classes and visibility keywords like private and protected.

Example of Closures in JavaScript:

const greeting = "Hello, ";

const sayHello = (name) => {
    return greeting + name;

console.log(sayHello("Alice")); // Output: Hello, Alice

PHP Closure:

$greeting = "Hello, ";

$sayHello = function($name) use ($greeting) {
    return $greeting . $name;

echo $sayHello("Alice"); // Output: Hello, Alice

33. What is late static binding? Explain the behavior and usage of static.

Late Static Binding:

Late static binding is a feature in PHP that allows classes to reference the correct class context, even in situations where inheritance and overridden methods are involved. It addresses the issue of determining the appropriate class at runtime when using self:: or parent:: inside a method of a class hierarchy.


Consider a scenario where a parent class defines a method, and a child class overrides it. If the overridden method uses self:: to refer to the method, it will always reference the method in the parent class, even when called on an instance of the child class. Late static binding solves this by allowing static:: to reference the class where the method is actually called.

Usage of static:

  1. Overriding Methods: When you override a method in a child class, you can use static:: to refer to the class context where the method is called. This ensures that the correct method implementation is used, regardless of the class instance.

  2. Factory Methods: static is often used in factory methods, where a class creates instances of its subclasses. This allows the factory method to instantiate the appropriate subclass dynamically.

  3. Static Method Inheritance: When you have a static method in a parent class and want to call it from a child class, using static:: ensures that the correct class context is used.


class ParentClass {
    public static function getInfo() {
        return "Parent class info";

class ChildClass extends ParentClass {
    public static function getInfo() {
        return "Child class info";

    public static function getInheritedInfo() {
        return parent::getInfo(); // Calls ParentClass::getInfo()

    public static function getLateBoundInfo() {
        return static::getInfo(); // Calls either ParentClass::getInfo() or ChildClass::getInfo() based on context

echo ChildClass::getInheritedInfo(); // Output: "Parent class info"
echo ChildClass::getLateBoundInfo(); // Output: "Child class info"

In this example, getInheritedInfo() uses parent:: to reference the parent class's method, while getLateBoundInfo() uses static:: to reference the method based on the calling context.

34. How can you override session storage?

Overriding Session Storage:

In PHP, you can override the default session storage mechanism by implementing a custom session handler. This allows you to store session data in a location other than the default file-based storage, such as a database, caching system, or external storage service. Custom session handlers give you control over how session data is read, written, and managed.

Steps to Override Session Storage:

  1. Implement Custom Session Handler Class: Create a class that implements the SessionHandlerInterface interface. This interface defines methods for opening, reading, writing, and closing sessions.

  2. Register the Custom Session Handler: Set your custom session handler as the active session handler using the session_set_save_handler() function.

Example - Custom Database Session Handler:

class DatabaseSessionHandler implements SessionHandlerInterface {
    // Implement methods like open, close, read, write, destroy, gc

$handler = new DatabaseSessionHandler();
session_set_save_handler($handler, true);

Configuration Option session.save_handler:

The session.save_handler configuration option in PHP allows you to specify the type of session storage mechanism you want to use for storing session data. This option determines how session data is managed and stored between user requests. It is used to set the session storage handler that PHP will use to handle session data.


The session.save_handler option can have various values, each corresponding to a different session storage mechanism:

  1. "files" (Default): Session data is stored in files on the server's file system.

  2. "memcached": Session data is stored using the Memcached extension.

  3. "redis": Session data is stored using the Redis extension.

  4. "custom": You can specify a custom session handler using the session_set_save_handler() function.


// Set the session save handler to Memcached
ini_set('session.save_handler', 'memcached');
ini_set('session.save_path', 'localhost:11211'); // Memcached server address

// Start the session

// Session data will now be stored using Memcached

Important Considerations:

  1. Extension Requirements: Some session handlers require specific PHP extensions (e.g., Memcached or Redis) to be installed and enabled on the server.

  2. Custom Handlers: If you want to implement a custom session handler, you can set session.save_handler to "custom" and use the session_set_save_handler() function to register your custom handler.

  3. Security: Ensure that your chosen session storage mechanism is secure and suitable for your application's requirements.

  4. Compatibility: When changing the session save handler, consider potential impacts on existing session data and application behavior.

35. Tell me about the SPL library (Reflection, autoload, data structures).

SPL Library (Standard PHP Library):

The SPL (Standard PHP Library) is a collection of built-in classes and interfaces in PHP that provides a set of powerful and standardized features to work with various data structures, manipulate files, handle exceptions, and more. It enhances PHP's capabilities and promotes consistent programming practices.


  • The Reflection classes in SPL allow you to inspect and manipulate classes, interfaces, methods, and properties at runtime. They provide reflection capabilities, making it possible to analyze the structure of classes and their members programmatically.

  • Reflection is useful for creating tools like documentation generators, debugging aids, and frameworks that rely on introspection.


  • The SPL Autoload feature enables automatic loading of classes without the need to manually include or require files. It helps manage the inclusion of class files on-demand when classes are used.

  • The spl_autoload_register() function is used to register autoload functions, which are called when a class is not yet defined, allowing you to include the necessary file.

Data Structures:

SPL provides various data structures that offer advanced functionality beyond basic arrays:

  1. SplQueue: A double-ended queue, allows elements to be inserted and removed from both ends efficiently.

  2. SplStack: A stack implementation based on a doubly linked list.

  3. SplDoublyLinkedList: A doubly linked list that can be used as both a stack and a queue.

  4. SplHeap: An abstract base class for implementing heaps (priority queues).

  5. SplFixedArray: An array-like structure with a fixed size, offering faster access and iteration compared to standard arrays.

  6. SplObjectStorage: A map-like container that associates objects with data or metadata.

  7. ArrayObject: Extends the built-in array to provide additional methods and features.

Example - Autoload:

// Register an autoloader function
spl_autoload_register(function($class) {
    include 'classes/' . $class . '.php';

// Now you can use classes without manually including files
$myObject = new MyClass();

Example - SplQueue:

$queue = new SplQueue();

echo $queue->dequeue(); // Output: "item1"

Example - Using Reflection to Inspect a Class:

class MyClass {
    public $property;
    private function method() {}

$reflection = new ReflectionClass('MyClass');

$properties = $reflection->getProperties();
$methods = $reflection->getMethods();

foreach ($properties as $property) {
    echo $property->getName(); // Output: property

foreach ($methods as $method) {
    echo $method->getName(); // Output: method

Example - Using ArrayObject:

$array = new ArrayObject(['apple', 'banana', 'cherry']);

echo $array[2]; // Output: cherry


The spl_autoload_register function simplifies the process of automatically loading class files when they are required in your PHP code. It is used for implementing class autoloading, which eliminates the need to manually include or require class files before using them.

How spl_autoload_register Works:

  1. You define a custom autoload function that takes the class name as a parameter and includes the corresponding class file.

  2. You register this autoload function using the spl_autoload_register function.

When a class is used in your code that hasn't been defined yet, PHP triggers the registered autoload function(s) to attempt to load the class file based on its name. This mechanism allows you to follow an on-demand approach to loading classes, improving code organization and reducing the need for explicit file includes.

// Define an autoload function
function myAutoloader($className) {
    include 'classes/' . $className . '.php';

// Register the autoload function

// Now you can use classes without manual includes
$myObject = new MyClass();

36. Tell me about the SOLID principles.

  1. Single Responsibility Principle (SRP):

    • A class should have only one reason to change, meaning it should have a single responsibility.

    • Example: A User class should handle user data, not email notifications.

  2. Open/Closed Principle (OCP):

    • Software entities (classes, modules, functions) should be open for extension but closed for modification.

    • Example: Instead of modifying existing code, new behavior is added through inheritance or composition.

  3. Liskov Substitution Principle (LSP):

    • Subtypes must be substitutable for their base types without affecting the correctness of the program.

    • Example: Derived classes should honor the contract of the base class and not introduce unexpected behaviors. A Square should be a valid substitute for a Rectangle.

  4. Interface Segregation Principle (ISP):

    • Clients should not be forced to depend on interfaces they do not use. Keep interfaces focused and specific.

    • Example: Splitting a large interface into smaller, more specialized interfaces for different client needs. Instead of a monolithic Worker interface, split it into Cook and Driver interfaces.

  5. Dependency Inversion Principle (DIP):

    • High-level modules should not depend on low-level modules. Both should depend on abstractions.

    • Example: Rather than depending on concrete classes, classes should depend on interfaces or abstract classes. Instead of directly creating database connections, use an interface and inject implementations.


// Single Responsibility Principle
class UserManager {
    public function createUser($userData) {
        // Create user logic

// Open/Closed Principle
interface Shape {
    public function area();

class Circle implements Shape {
    public function area() {
        // Calculate circle area

// Liskov Substitution Principle
class Bird {
    public function fly() {
        // Bird flying logic

class Sparrow extends Bird {
    public function fly() {
        // Sparrow flying logic

// Interface Segregation Principle
interface Worker {
    public function work();

class Cook implements Worker {
    public function work() {
        // Cook's work

// Dependency Inversion Principle
interface Database {
    public function query($sql);

class MySQLDatabase implements Database {
    public function query($sql) {
        // MySQL query

37. Explain the Dependency Inversion Principle and what specifically differentiates it from the traditional Dependency Flow.

The term "Dependency Inversion" might sound a bit counterintuitive at first, but it refers to a shift in the way dependencies are managed within a software system. To understand why it's called "inversion," let's break down the concept.

Traditionally, in software development, dependencies between components are managed in a top-down manner. Higher-level modules depend on lower-level modules. For example, a high-level module might directly use or create instances of lower-level classes.

The Dependency Inversion Principle (DIP) suggests inverting this traditional dependency direction. Instead of high-level modules depending directly on low-level modules, both high-level and low-level modules should depend on abstractions (interfaces or abstract classes). This inversion changes the way the system is structured and how components interact.

The term "inversion" comes from the reversal of the dependency direction. It's a shift from high-level modules controlling the lower-level ones to a design where both high-level and low-level modules adhere to a common set of abstractions. This inversion has several benefits, including improved flexibility, modularity, and easier maintenance.

In simpler terms:

  • Traditional Dependency Flow: High-level modules control low-level modules.

  • Dependency Inversion: Both high-level and low-level modules adhere to common abstractions.

By inverting the direction of dependency, you create a more decoupled and flexible architecture where changes in low-level components don't necessarily impact high-level components, and vice versa. This promotes modular design, reusability, and maintainability.


Imagine a user authentication system:

Traditional Dependency Flow:

  • A high-level UserService directly depends on a low-level Database class to manage user data.

  • Changes in the Database implementation could affect the UserService functionality.

Dependency Inversion Principle:

  • A UserService depends on an DatabaseInterface (an abstraction).

  • The Database class implements the DatabaseInterface.

  • Changes in the Database implementation are confined to the implementation class and don't directly affect the UserService.

38. Tell me about the GRASP patterns.

GRASP (General Responsibility Assignment Software Patterns):

GRASP is a set of principles and patterns used in object-oriented design to guide the assignment of responsibilities to classes and objects within a software system. These patterns help developers make informed decisions about the structure of their code, leading to more maintainable and flexible designs.

In simpler terms: imagine you're organizing a team to build a robot. Each team member has a specific role that they're good at. Similarly, GRASP patterns help you assign the right jobs to classes in software design to make your code organized and effective.

Key GRASP Patterns:

  1. Information Expert:

    • Assign a responsibility to the class with the necessary information to fulfill it.

    • Encourages placing methods that require specific information inside the class that holds that information.

    • Like choosing a teammate who knows the most about a task, assign a class the job if it has the data needed to do it.

    • Example: A Student class should calculate their GPA because it has the necessary grades.

  2. Creator:

    • Assign the responsibility of creating an instance of a class to the class that has the necessary information.

    • Avoids spreading object creation logic across multiple classes.

    • Just like the person who knows how to build something should do it, assign creating objects to a class that knows about them.

    • Example: A Library class could create instances of Book objects since it knows the book details.

  3. Controller:

    • Assign the responsibility of handling system events (such as user input) to a class that represents a use case scenario or a user action.

    • Acts as an intermediary between the user interface and the rest of the system.

    • Think of a team captain organizing tasks. Assign managing user actions to a class that coordinates what should happen.

    • Example: A GameController class could handle user input and update the game state.

  4. Polymorphism:

    • Assign a responsibility to a class that makes use of polymorphism to differentiate between different types of objects.

    • Encourages designing interfaces or base classes that allow for varying implementations.

    • Like using different tools for different tasks, assign a class that can handle different types of things using polymorphism.

    • Example: An Animal interface could be used for different animals like Dog and Cat.

  5. Pure Fabrication:

    • Introduce a class that doesn't represent a concept in the problem domain but serves as a helper or manager to achieve low coupling and high cohesion.

    • Used to avoid violating other GRASP principles.

    • Sometimes you need a helper who doesn't fit a specific role. Create a class just for helping, even if it doesn't match the real world.

    • Example: A Logger class could help manage logging even though it's not a real-world thing.

  6. Indirection:

    • Introduce an intermediate class or interface to provide indirection between other components, reducing coupling.

    • Helps in achieving flexibility and avoiding tight dependencies.

    • Think of a secretary passing messages between people. Introduce a class to pass messages or tasks between other classes.

    • Example: An EventDispatcher class could manage communication between different parts of your program.

  7. Protected Variations:

    • Design components in a way that variations or changes in one component do not affect other components.

    • Use interfaces or abstract classes to define stable points of interaction between components.

    • Like using a buffer to protect delicate items, design your classes so changes in one part don't affect others.

    • Example: Use interfaces to communicate between different parts of your system, shielding them from changes.

  8. High Cohesion:

    • Assign responsibilities in a way that elements within a class or module are closely related and focused on a single task.

    • Helps in creating more understandable and maintainable code.

    • Like having a team member focused on one task at a time, assign jobs to a class that make sense together.

    • Example: A PaymentProcessor class should only handle payments, not unrelated tasks.

Benefits of GRASP Patterns:

  • Clear Roles: Assign clear responsibilities to classes, like giving clear roles to team members.

  • Easy Changes: Make changes in one place without affecting everything else, just like a team member changing their role.

  • Organized Code: Keep your code well-structured, making it easier for you and your teammates to understand.

39. Tell me about Dependency Injection: What is a DI container? What are the implementation options?

Dependency Injection (DI):

Imagine you're cooking in a kitchen, and instead of searching for ingredients yourself, someone hands you the right ingredients at the right time. Dependency Injection is like that for software: it's a way to give a class the things it needs rather than making it find them on its own.

DI Containers:

A Dependency Injection (DI) container is like a helper chef in the kitchen. It manages the ingredients (dependencies) and serves them to your classes when needed. It helps keep your code organized and saves you from searching for ingredients everywhere.

Implementation Options:

  1. Manual Dependency Injection:

    • You provide the dependencies to a class through its constructor or methods.

    • Like handing over ingredients directly to a chef.

    • Simple and clear but can become cumbersome in large projects.

  2. Constructor Injection:

    • You pass dependencies to a class through its constructor.

    • The class can't work without these dependencies.

    • Like giving a recipe to a chef along with the needed ingredients.

  3. Setter Injection:

    • You use methods (setters) to provide dependencies after the class is created.

    • Useful for optional dependencies.

    • Like giving a chef extra ingredients later if they want to experiment.

  4. Method Injection:

    • You pass dependencies directly to the methods that need them.

    • Useful for methods that need different dependencies.

    • Like giving a chef specific spices for different dishes.

  5. DI Containers:

    • A DI container is like an ingredient storage and distributor.

    • It manages the creation and provision of dependencies.

    • You configure the container with how to create and provide each dependency.

    • Like having a kitchen helper who prepares and brings ingredients as needed.

Benefits of DI and DI Containers:

  • Flexibility: You can easily change or upgrade dependencies without changing the class code.

  • Testability: You can provide mock or fake dependencies for testing.

  • Modularity: Code becomes more modular and easier to understand.

  • Separation of Concerns: Each class focuses on its job without worrying about finding dependencies.


Consider a UserService class that needs a database connection. With DI:

class UserService {
    private $database;

    public function __construct(DatabaseInterface $database) {
        $this->database = $database;

    public function getUser($userId) {
        // Use $this->database->query() to fetch user data

In this example, the DatabaseInterface is injected into UserService through its constructor, ensuring it has the required dependency.

DI Containers, like Symfony's Dependency Injection Component or Laravel's Service Container, automate this process and make managing dependencies across your application much more convenient.

40. What do you know about MVC?

MVC (Model-View-Controller):

Imagine you're building a house. You have architects who design the layout, workers who build, and you who make decisions. MVC is a similar concept for building software. It separates different aspects of your code so it's organized and easier to manage.


  • The Model is like the blueprint of the house.

  • It manages data and logic of your application.

  • Like storing information about users, products, or any data you need.


  • The View is like the windows and doors of the house.

  • It's responsible for displaying data to users.

  • Like showing a webpage, a piece of text, or an image.


  • The Controller is like you, making decisions for the house.

  • It handles user input and directs the model and view.

  • Like taking user requests and telling the model to fetch data and the view to display it.

Benefits of MVC:

  • Separation of Concerns: Each part does its own job without mixing up.

  • Modularity: Easier to understand and change one part without affecting the others.

  • Reusability: You can reuse models and views for different parts of your app.

  • Collaboration: Different team members can work on different parts without conflicts.


Imagine you're making a To-Do List app:

  • Model: Manages the tasks and their status (done/undone).

  • View: Displays the list of tasks to the user.

  • Controller: Handles adding tasks, marking tasks as done, and updating the view.

With MVC, your code becomes organized, making it easier to build and maintain software, just like how a well-structured house is easier to manage and live in.

42. What do you know about GoF patterns?

GoF Patterns (Gang of Four Design Patterns):

Think of GoF patterns like a set of building blocks for constructing complex structures with LEGO. These patterns were defined by a group of four authors (the Gang of Four) to provide solutions for common design problems in software development.

Creational Patterns:

  1. Factory Method:

    • Like a toy factory that produces different toys based on the request.

    • Creates objects without specifying their exact class.

  2. Abstract Factory:

    • Like a toy factory that produces families of related toys.

    • Creates object families without specifying their classes.

  3. Singleton:

    • Like a president's office that's accessed by everyone.

    • Ensures a class has only one instance and provides a global point of access.

  4. Builder:

    • Like a chef who assembles complex dishes from ingredients.

    • Separates construction of complex objects from their representation.

  5. Prototype:

    • Like a photocopy machine that creates copies of a document.

    • Creates new objects by copying existing ones.

Structural Patterns:

  1. Adapter:

    • Like a power adapter that lets you use devices from different countries.

    • Converts the interface of one class into another interface the client expects.

  2. Bridge:

    • Like a remote control that operates different devices.

    • Decouples abstraction from implementation.

  3. Composite:

    • Like a folder that can contain files or subfolders.

    • Composes objects into tree structures to represent part-whole hierarchies.

  4. Decorator:

    • Like adding toppings to a pizza.

    • Attaches additional responsibilities to an object dynamically.

  5. Facade:

    • Like a receptionist who handles calls and directs visitors.

    • Provides a unified interface to a set of interfaces in a subsystem.

  6. Flyweight:

    • Like a shared office space with common facilities.

    • Reduces memory usage by sharing common data among multiple objects.

  7. Proxy:

    • Like an ATM proxy that allows you to access your bank account.

    • Provides a surrogate or placeholder for another object to control access.

Behavioral Patterns:

  1. Chain of Responsibility:

    • Like a chain of managers approving expenses.

    • Allows more than one object to handle a request.

  2. Command:

    • Like a remote control that issues commands to devices.

    • Turns a request into a stand-alone object containing all information.

  3. Interpreter:

    • Like translating a language for someone.

    • Provides a way to evaluate language grammar or expressions.

  4. Iterator:

    • Like a vending machine that gives you items one by one.

    • Provides a way to access elements of a collection without exposing its underlying representation.

  5. Mediator:

    • Like a chatroom where people communicate through a central system.

    • Reduces direct connections between objects by using a mediator object.

  6. Memento:

    • Like a snapshot in time that you can return to.

    • Captures and restores an object's internal state.

  7. Observer:

    • Like subscribers receiving updates from a news source.

    • Defines a dependency between objects so that when one changes, others are notified.

  8. State:

    • Like a traffic light changing colors.

    • Allows an object to change its behavior when its internal state changes.

  9. Strategy:

    • Like using different algorithms to solve a problem.

    • Defines a family of algorithms, encapsulates each one, and makes them interchangeable.

  10. Template Method:

    • Like a recipe with steps that can vary.

    • Defines the structure of an algorithm, letting subclasses override specific steps.

  11. Visitor:

    • Like a museum visitor appreciating different exhibits.

    • Lets you add further operations to objects without having to modify them.

Benefits of GoF Patterns:

  • Proven Solutions: GoF patterns offer tried and tested solutions to recurring design problems.

  • Common Language: Developers can communicate design concepts more effectively using recognized patterns.

  • Flexibility: Patterns promote code that's easier to modify and extend.

  • Best Practices: Patterns embody best practices and principles of object-oriented design.

43. What do you know about patterns used in ORM (Object-Relational Mapping)?

Patterns in ORM (Object-Relational Mapping):

Think of ORM patterns as translators between different languages. ORM helps bridge the gap between object-oriented code and relational databases. These patterns provide guidelines for mapping objects to database tables and vice versa.

Active Record:

  • Like a two-way translator who speaks both languages.

  • Each class represents a database table, and instances of the class correspond to rows.

  • Directly ties business logic with database interactions.

Data Mapper:

  • Like having a dedicated translator and separate document for each language.

  • Separates database access and business logic into different classes.

  • Manages the mapping between objects and database tables.

Identity Map:

  • Like a map marking locations you've visited.

  • Ensures that each object is only loaded once into memory, preventing duplication.

  • Helps maintain consistency and avoids performance issues.

Unit of Work:

  • Like a shopping cart that tracks items before you check out.

  • Manages the state of objects during a business transaction.

  • Keeps track of changes and commits them to the database all at once.

Lazy Loading:

  • Like loading a webpage with images only when you scroll down.

  • Delays loading related objects until they're actually needed.

  • Helps improve performance by loading data on-demand.

Query Object:

  • Like a pre-written letter with specific questions.

  • Represents a database query as an object, allowing for more dynamic queries.

  • Enhances code reusability and readability.


  • Like a library that manages books.

  • Acts as a collection of objects, abstracting away the data access layer.

  • Provides a clean interface for querying and storing objects.

Benefits of ORM Patterns:

  • Abstraction: Patterns hide complex database interactions, making code more readable.

  • Modularity: Helps separate database concerns from business logic.

  • Efficiency: Optimizes database interactions and reduces repetitive code.

  • Consistency: Ensures uniformity in data access throughout the application.


Consider an ORM library like Eloquent in Laravel:

  • Active Record: A User model directly corresponds to a users table, and you can use it to both retrieve and save data.

  • Data Mapper: Eloquent's User model separates data access methods from the model itself, providing more flexibility.

  • Identity Map: Eloquent tracks instances of models that have been retrieved, preventing unnecessary database queries.

  • Unit of Work: Eloquent's save() method keeps track of changes and updates the database accordingly when you're ready.

  • Lazy Loading: Eloquent can load related data only when you access it, reducing unnecessary data retrieval.

  • Query Object: Eloquent provides methods like where() and orderBy() that generate query objects for dynamic queries.

  • Repository: The User model acts as a repository, providing methods to interact with the users table.

ORM patterns simplify the process of working with databases in an object-oriented environment, much like a translator helps you communicate in a foreign country.

44. Provide an example of implementing the Singleton pattern in PHP

class MusicPlayer {
    private static ?MusicPlayer $instance = null;
    private array $playlist = [];

    private function __construct() {
        // Private constructor prevents direct instantiation

    public static function getInstance(): MusicPlayer {
        if (self::$instance === null) {
            self::$instance = new MusicPlayer();
        return self::$instance;

    // Add a song to the playlist
    public function addSong($song) {
        $this->playlist[] = $song;

    // Get the current playlist
    public function getPlaylist(): array {
        return $this->playlist;

    // Magic method to prevent cloning
    private function __clone() {}

    // Magic method to prevent serialization
    private function __wakeup() {}

// Usage
$player = MusicPlayer::getInstance();
$player->addSong("Song 1");
$player->addSong("Song 2");

// Same instance, same playlist
$anotherPlayer = MusicPlayer::getInstance();
var_dump($anotherPlayer === $player);  // Output: bool(true)
var_dump($anotherPlayer->getPlaylist());  // Output: array(2) { [0]=> string(7) "Song 1" [1]=> string(7) "Song 2" }

In this example:

  • The MusicPlayer class follows the Singleton pattern with the getInstance() method.

  • We've added a private $playlist property to demonstrate instance-specific data.

  • Magic methods __clone() and __wakeup() are declared private to prevent cloning and serialization.

  • Performance optimization is achieved by creating the instance only when necessary.

  • The same instance is returned for subsequent calls to getInstance().

45. What's new in PHP 8?

PHP 8 New Features:

  1. Named Arguments:

    • Like giving specific instructions in a recipe.

    • Allows passing arguments to functions based on their parameter names, improving code readability.

  2. Attributes:

    • Like adding labels to items in a store.

    • Provides a way to add metadata and annotations to classes, methods, and properties.

  3. Constructor Property Promotion:

    • Like streamlining the setup process of a new home.

    • Allows declaring and initializing properties directly in the constructor parameters.

  4. Union Types:

    • Like saying a variable can be either a cat or a dog.

    • Lets you specify multiple possible types for function parameters and return values.

  5. Match Expression:

    • Like choosing the best outfit based on the weather.

    • Offers a more robust and readable alternative to the switch statement.

  6. Nullsafe Operator:

    • Like checking if you have an umbrella before going out in the rain.

    • Simplifies navigating through nested object properties when dealing with potential null values.

  7. New Built-in Types:

    • Like adding new ingredients to your kitchen.

    • Introduces mixed, static, and never as built-in types to enhance type flexibility.

  8. JIT Compilation:

    • Like having a supercharged engine in your car.

    • Improves performance by adding Just-In-Time compilation, making PHP execution faster.

  9. Improvements to Error Handling:

    • Like having a better GPS system while driving.

    • Provides more detailed error messages and better handling of errors and exceptions.

  10. Consistent 64-bit Support:

    • Like having a larger desk to work on.

    • Ensures consistent integer and float sizes on all platforms, making code more reliable.

  11. Improvements to the mysqli Extension:

    • Like upgrading your toolbox with new tools.

    • Enhances features and performance in the mysqli extension.

  12. New Functions and Classes:

    • Like adding new gadgets to your toolkit.

    • Introduces new functions like str_contains(), str_starts_with(), and new classes like Stringable.

Previous articles of the series:

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 1-15.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 16-30.