Table of Contents

3. Objects & Data Transfer Objects (DTOs) — Representing Data in Modern PHP

Why this matters

Modern PHP uses objects not just for behavior, but for clarity of data.
In contrast, AI often generates arrays everywhere — associative arrays for input, output, configuration, responses, and even domain data (see DTO example below).

But arrays:

DTOs solve this by giving shape to our data.

Understanding when to use objects — and when a DTO is the right tool — helps us keep our code predictable, explicit, and easy to review.

1. Objects represent behavior + state

A traditional object bundles:

Example: 

class User {
    public function __construct(
        public string $name,
        public string $email,
    ) {}
 
    public function greet(): string {
        return "Hello, {$this->name}";
    }
}

Objects are ideal when:

AI often generates objects with no behavior
— which is a sign that a DTO might be more appropriate.

2. DTOs represent pure data

A Data Transfer Object is a simple, structured container for data — no behavior, no logic, no side effects.

Example: 

class UserData {
    public function __construct(
        public string $name,
        public string $email,
    ) {}
}
DTOs are ideal when we - are passing data between layers,
- want type safety,
- want predictable structure,
- want to avoid “stringly‑typed” arrays

DTOs make our code self‑documenting.

3. Why DTOs are better than arrays

Associative arrays are flexible — too flexible.

Arrays:

DTOs:

AI often defaults to arrays because
they’re easy to generate.

Our mental model helps us replace them with DTOs
where structure matters.

4. Promotion makes DTOs effortless

PHP 8 introduced constructor property promotion: 

class ProductData {
    public function __construct(
        public int $id,
        public string $name,
        public float $price,
    ) {}
}

This turns DTOs into a first‑class citizen of modern PHP:

This is one of the most important modern PHP idioms.

5. DTOs are not entities

A DTO:

An entity:

AI often confuses these two
— generating DTOs where entities belong, or vice‑versa.

Our understanding helps us keep the architecture clean.

6. When to use a DTO

Use a DTO when we need:

DTOs shine when we want clarity without behavior.

7. When not to use a DTO

Avoid DTOs when:

In those cases, use a real object
— an entity or value object.

8. When AI gets this wrong

AI often defaults to associative arrays for everything — input, output, configuration, even domain data. This works, but it hides structure and makes mistakes harder to see. Our mental model helps us notice when an array should really be a DTO, especially in places where shape, clarity, or type safety matter.

Summary

Modern PHP uses objects for behavior and DTOs for structure.

DTOs give us:

Once we internalize this, we can immediately see when AI‑generated code is relying too heavily on arrays — or using objects where a DTO would be cleaner.