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:

• have no structure
• have no guarantees
• are easy to misuse
• hide mistakes until runtime

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.

A traditional object bundles:

• state (properties)
• behavior (methods)

Example:

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

Objects are ideal when:

• the data has meaning
• the data has rules
• the data has behavior
• the data belongs to a domain concept

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

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 make our code self‑documenting.

Associative arrays are flexible — too flexible.

Arrays:

• allow missing keys
• allow extra keys
• allow wrong types
• allow silent failures
• hide mistakes

DTOs:

• enforce structure
• enforce types
• make intent visible
• fail early and predictably
• integrate cleanly with static analysis

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

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

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:

• minimal boilerplate
• clear structure
• strong typing
• easy to read
• easy to maintain

This is one of the most important modern PHP idioms.

A DTO:

• has no behavior
• has no identity
• has no lifecycle
• is not tied to persistence

An entity:

• has identity
• has rules
• has behavior
• belongs to a domain

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

Our understanding helps us keep the architecture clean.

Use a DTO when we need:

• structured input
• structured outputAPI request/response objects
• form data
• query results
• configuration objects
• data passed between layers

DTOs shine when we want clarity without behavior.

Avoid DTOs when:

• the data has rules
• the data has invariants
• the data has behavior
• the data belongs to a domain concept

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

Modern PHP uses objects for behavior and DTOs for structure.

DTOs give us:

• clarity
• type safety
• predictable shape
• self‑documenting code
• fewer runtime surprises

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.

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