Tools for building rich domain primitives in PHP.

Installation

composer require fasano/phprimitives

What is this?

PHP has no base class for scalars - so there's nowhere to hook validation, enforce invariants, or express domain meaning. PHPrimitives fills that gap with 4 base classes:

• AbstractString
• AbstractInteger
• AbstractFloat
• AbstractBoolean

How to use them?

Simply extend the base classes, and implement the validate method. Throw an InvalidArgumentException if the value is invalid.

readonly class Email extends AbstractString
{
    protected static function validate(string $value): void
    {
        if (!filter_var($value, FILTER_VALIDATE_EMAIL)) {
            throw new InvalidArgumentException('Invalid email address: ' . $value);
        }
    }
}

Why use them?

Primitives enforce invariants at the edges of your application. Validate at boundaries, trust everywhere else. Primitives convert to/from scalars at your application edges:

# Input boundary - scalar to primitive
$age = new Age($request->input('age'));           # Throws if invalid
$email = new Email($request->input('email'));     # Throws if invalid

# Everywhere else - work with primitives
function createUser(Email $email, Age $age): User
{
    # Type system guarantees correctness
    # No defensive checks required
}

# Output boundary - primitive to scalar
$repository->save([
    'email' => $email->value,
    'age' => $age->value,
]);

Without primitives, validation scatters throughout your codebase:

function createUser(string $email, int $age): void
{
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) { /* ... */ }
    if ($age < 0 || 120 < $age) { /* ... */ }
    # Repeat in every function that touches these values
}

Key benefits:

• Invariants enforced at construction — Invalid data cannot enter your domain
• Type safety through nominal typing — Can't pass Age where Temperature is expected, even though both wrap integers
• Domain concepts expressed clearly — Email is more meaningful than string

Serialization

Primitives implement JsonSerializable out of the box:

echo json_encode(new Person(
    new Name('John'),
    new Age(18),
    new Email('john@example.com'),
));
// {"name":"John","age":18,"email":"john@example.com"}

Ecosystem

The wrapping and unwrapping of values into primitive objects can be automated fairly trivially. You can find very simple libs to do so in Symfony and Doctrine below, along with a full example project that uses no scalars anywhere.

Package	Description
phprimitives-doctrine	Doctrine DBAL type mappings
phprimitives-symfony	Symfony Serializer integration
phprimitives-example	An in-context example usage of PHPrimitives