Backend PHP Type Safety

Backend PHP Type Safety

When to use this skill

• Building type-safe applications
• Preventing type-related bugs
• Using static analysis tools
• Writing maintainable code

Workflow

• Enable strict_types in all files
• Type hint all parameters
• Declare return types
• Use PHPStan or Psalm
• Avoid mixed types

Instructions

Strict Types

<?php

declare(strict_types=1);

// Now type coercion is disabled
function add(int $a, int $b): int
{
    return $a + $b;
}

add(1, 2);    // OK
// add('1', '2'); // TypeError in strict mode

Property Types

<?php

declare(strict_types=1);

class User
{
    private int $id;
    private string $email;
    private ?string $phone = null;
    private array $roles = [];

    public function __construct(int $id, string $email)
    {
        $this->id = $id;
        $this->email = $email;
    }
}

Return Type Declarations

<?php

declare(strict_types=1);

class UserService
{
    public function getUser(int $id): ?User
    {
        $user = $this->repository->find($id);
        return $user; // Can be User or null
    }

    public function getAllUsers(): array
    {
        return $this->repository->findAll();
    }

    public function createUser(array $data): User
    {
        // Must return User, not null
        return $this->repository->create($data);
    }
}

Generic Collections with PHPDoc

<?php

declare(strict_types=1);

class UserRepository
{
    /**
     * @return array<User>
     */
    public function findAll(): array
    {
        // PHPStan knows this returns array of User objects
        return [];
    }

    /**
     * @param array<int> $ids
     * @return array<User>
     */
    public function findByIds(array $ids): array
    {
        return [];
    }
}

Static Analysis (PHPStan)

# Install
composer require --dev phpstan/phpstan

# Run
vendor/bin/phpstan analyse app

# phpstan.neon
parameters:
    level: 8
    paths:
        - app

Resources

• Always enable strict_types
• Type hint everything
• Use static analysis in CI/CD
• PHPStan level 8 for maximum safety