Constructors

Quick Introduction

Constructors is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only constructors — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the Employee Management. After a user signs in, you need constructors working correctly before storing data or showing a dashboard.

Without understanding Constructors, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• Constructors is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (Employee Management) uses constructors in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for Constructors. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

readonly class DatabaseConfig {
    public function __construct(
        public string $host,
        public int $port,
        public string $database,
        public string $username,
        public string $password,
    ) {}

    public static function fromEnv(): self {
        return new self(
            host: getenv('DB_HOST') ?: '127.0.0.1',
            port: (int)(getenv('DB_PORT') ?: 3306),
            database: getenv('DB_NAME') ?: 'app',
            username: getenv('DB_USER') ?: 'root',
            password: getenv('DB_PASS') ?: '',
        );
    }
}

print_r(DatabaseConfig::fromEnv());

Line by line

1. — part of the constructors example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. readonly class DatabaseConfig { — part of the constructors example; run the file to see the result.
4. public function __construct( — part of the constructors example; run the file to see the result.
5. public string $host, — part of the constructors example; run the file to see the result.

User #42 (user@example.com) balance $19.99

Real-World Example

In the Employee Management, constructors appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: Constructors exercise for Employee Management