PHP Specialist

PHP Specialist

Overview

Write modern, type-safe, and maintainable PHP 8.x code adhering to PSR standards and SOLID principles. This skill covers the full modern PHP toolchain: language features introduced in PHP 8.0 through 8.4, PSR interoperability standards, Composer dependency management, static analysis with PHPStan and Psalm, coding style enforcement with PHP CS Fixer and Pint, and architectural patterns that leverage the type system for correctness at compile time rather than runtime.

Apply this skill whenever PHP code is being written, reviewed, or refactored in any framework or standalone context.

Multi-Phase Process

Phase 1: Environment Assessment

1. Identify PHP version from composer.json -> require.php
2. Review composer.json for autoloading strategy (PSR-4 namespaces)
3. Check for static analysis configuration (phpstan.neon, psalm.xml)
4. Identify coding standard tool (pint.json, .php-cs-fixer.php)
5. Catalog existing patterns: enums, DTOs, value objects, interfaces

STOP — Do NOT write code without knowing the PHP version and autoloading strategy.

Phase 2: Design

1. Define interfaces and contracts before implementations
2. Design value objects and DTOs with readonly properties
3. Map domain concepts to backed enums where applicable
4. Plan exception hierarchy for the domain
5. Identify seams for dependency injection

STOP — Do NOT implement without interfaces defined for key boundaries.

Phase 3: Implementation

1. Write interfaces first — contracts before concrete classes
2. Implement with constructor promotion, readonly properties, union/intersection types
3. Use match expressions over switch; named arguments for clarity
4. Leverage first-class callable syntax for functional composition
5. Apply SOLID principles at every class boundary

STOP — Do NOT skip strict_types declaration in any PHP file.

Phase 4: Quality Assurance

1. Run PHPStan at maximum achievable level (target level 9)
2. Enforce coding style with PHP CS Fixer or Laravel Pint
3. Verify type coverage — no mixed without justification
4. Review for SOLID violations and code smells
5. Confirm Composer autoload is optimized (--classmap-authoritative)

PHP Version Feature Decision Table

Modern PHP 8.x Features

Enums (PHP 8.1+)

// Backed enum with methods — replaces class constants and magic strings
enum OrderStatus: string
{
    case Draft     = 'draft';
    case Pending   = 'pending';
    case Confirmed = 'confirmed';
    case Shipped   = 'shipped';
    case Delivered = 'delivered';
    case Cancelled = 'cancelled';

    public function label(): string
    {
        return match ($this) {
            self::Draft     => 'Draft',
            self::Pending   => 'Pending Review',
            self::Confirmed => 'Confirmed',
            self::Shipped   => 'Shipped',
            self::Delivered => 'Delivered',
            self::Cancelled => 'Cancelled',
        };
    }

    public function isFinal(): bool
    {
        return in_array($this, [self::Delivered, self::Cancelled], true);
    }

    /** @return list<self> */
    public static function active(): array
    {
        return array_filter(self::cases(), fn (self $s) => ! $s->isFinal());
    }
}

Readonly Properties and Classes (PHP 8.1 / 8.2)

// Readonly class — all properties are implicitly readonly
readonly class Money
{
    public function __construct(
        public int    $amount,
        public string $currency,
    ) {}

    public function add(self $other): self
    {
        if ($this->currency !== $other->currency) {
            throw new CurrencyMismatchException($this->currency, $other->currency);
        }

        return new self($this->amount + $other->amount, $this->currency);
    }

    public function isPositive(): bool
    {
        return $this->amount > 0;
    }
}

Constructor Promotion

class CreateUserAction
{
    public function __construct(
        private readonly UserRepository $users,
        private readonly Hasher         $hasher,
        private readonly EventDispatcher $events,
    ) {}

    public function execute(CreateUserData $data): User
    {
        $user = $this->users->create([
            'name'     => $data->name,
            'email'    => $data->email,
            'password' => $this->hasher->make($data->password),
        ]);

        $this->events->dispatch(new UserCreated($user));

        return $user;
    }
}

Named Arguments

// Improves readability for functions with many parameters or boolean flags
$user = User::create(
    name: $request->name,
    email: $request->email,
    isAdmin: false,
    sendWelcomeEmail: true,
);

// Particularly valuable with optional parameters
$response = Http::timeout(seconds: 30)
    ->retry(times: 3, sleepMilliseconds: 500, throw: true)
    ->get($url);

Match Expressions

// match is strict (===), exhaustive, and returns a value
$discount = match (true) {
    $total >= 10000 => 0.15,
    $total >= 5000  => 0.10,
    $total >= 1000  => 0.05,
    default         => 0.00,
};

// Replaces switch with no fall-through risk
$handler = match ($event::class) {
    OrderPlaced::class   => new HandleOrderPlaced(),
    PaymentFailed::class => new HandlePaymentFailed(),
    default              => throw new UnhandledEventException($event),
};

Union and Intersection Types

// Union type — accepts either type
function findUser(int|string $identifier): User
{
    return is_int($identifier)
        ? User::findOrFail($identifier)
        : User::where('email', $identifier)->firstOrFail();
}

// Intersection type — must satisfy all interfaces
function processLoggableEntity(Loggable&Serializable $entity): void
{
    $entity->log();
    $data = $entity->serialize();
}

// DNF types (PHP 8.2) — combine union and intersection
function handle((Renderable&Countable)|string $content): string
{
    if (is_string($content)) {
        return $content;
    }

    return $content->render();
}

First-Class Callable Syntax (PHP 8.1+)

// Create closures from named functions
$slugify = Str::slug(...);
$titles  = array_map($slugify, $names);

// Method references
$validator = Validator::make(...);

// Useful for pipeline / collection patterns
$activeUsers = collect($users)
    ->filter(UserPolicy::isActive(...))
    ->map(UserTransformer::toArray(...))
    ->values();

Fibers (PHP 8.1+)

// Fibers enable cooperative multitasking — foundation for async frameworks
$fiber = new Fiber(function (): void {
    $value = Fiber::suspend('paused');
    echo "Resumed with: {$value}";
});

$result = $fiber->start();        // Returns 'paused'
$fiber->resume('hello world');    // Prints: "Resumed with: hello world"

// Practical use: async HTTP client internals, event loops (Revolt, ReactPHP)
// Application developers rarely use Fiber directly — frameworks abstract it

PSR Standards

PSR-4 Autoloading

{
    "autoload": {
        "psr-4": {
            "App\\": "app/",
            "Domain\\": "src/Domain/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\\": "tests/"
        }
    }
}

Rule: namespace segment maps 1:1 to directory. App\Http\Controllers\UserController lives at app/Http/Controllers/UserController.php.

Composer Dependency Management

Essential Commands

Best Practices

• Always commit composer.lock — reproducible installs across environments
• Use ^ (caret) constraints: "laravel/framework": "^12.0" allows minor/patch updates
• Separate dev dependencies: testing, static analysis, and debug tools go in require-dev
• Run composer audit in CI to catch known vulnerabilities
• Use composer dump-autoload --classmap-authoritative in production for speed

Static Analysis

PHPStan Levels

PHPStan Configuration

# phpstan.neon
parameters:
    level: 9
    paths:
        - app
        - src
    excludePaths:
        - app/Console/Kernel.php
    ignoreErrors: []
    checkMissingIterableValueType: true
    checkGenericClassInNonGenericObjectType: true

includes:
    - vendor/larastan/larastan/extension.neon  # Laravel-specific rules

PHP CS Fixer / Pint

// .php-cs-fixer.php — for non-Laravel projects
return (new PhpCsFixer\Config())
    ->setRules([
        '@PER-CS'            => true,
        'strict_types'       => true,
        'declare_strict_types' => true,
        'ordered_imports'    => ['sort_algorithm' => 'alpha'],
        'no_unused_imports'  => true,
        'trailing_comma_in_multiline' => true,
    ])
    ->setFinder(
        PhpCsFixer\Finder::create()->in([__DIR__ . '/src', __DIR__ . '/tests'])
    );

For Laravel projects, use Pint with a pint.json preset — it wraps PHP CS Fixer with Laravel-specific defaults.

SOLID Principles in PHP

Dependency Inversion Example

// Contract (abstraction)
interface PaymentGateway
{
    public function charge(Money $amount, PaymentMethod $method): PaymentResult;
}

// Implementation (concretion) — can be swapped without changing consumers
final class StripeGateway implements PaymentGateway
{
    public function __construct(private readonly StripeClient $client) {}

    public function charge(Money $amount, PaymentMethod $method): PaymentResult
    {
        // Stripe-specific logic
    }
}

// Consumer depends on abstraction only
final class ProcessPaymentAction
{
    public function __construct(private readonly PaymentGateway $gateway) {}

    public function execute(Order $order): PaymentResult
    {
        return $this->gateway->charge($order->total, $order->paymentMethod);
    }
}

Error Handling Patterns

Custom Exception Hierarchy

// Base domain exception
abstract class DomainException extends \RuntimeException {}

// Specific exceptions with factory methods
final class InsufficientFundsException extends DomainException
{
    public static function forAccount(Account $account, Money $required): self
    {
        return new self(sprintf(
            'Account %s has %d %s but %d %s is required.',
            $account->id,
            $account->balance->amount,
            $account->balance->currency,
            $required->amount,
            $required->currency,
        ));
    }
}

Result Pattern (Error as Value)

/** @template T */
readonly class Result
{
    /** @param T|null $value */
    private function __construct(
        public bool    $ok,
        public mixed   $value = null,
        public ?string $error = null,
    ) {}

    /** @param T $value */
    public static function success(mixed $value): self
    {
        return new self(ok: true, value: $value);
    }

    public static function failure(string $error): self
    {
        return new self(ok: false, error: $error);
    }
}

// Usage — caller must handle both paths
$result = $action->execute($data);
if (! $result->ok) {
    return response()->json(['error' => $result->error], 422);
}

Type Safety Patterns

Branded / Opaque Types via Readonly Classes

// Prevent accidental mixing of IDs from different entities
readonly class UserId
{
    public function __construct(public int $value) {}

    public function equals(self $other): bool
    {
        return $this->value === $other->value;
    }
}

readonly class OrderId
{
    public function __construct(public int $value) {}
}

// Compiler prevents: processOrder(new UserId(1)) when OrderId is expected
function processOrder(OrderId $orderId): void { /* ... */ }

Generic Collections via PHPStan Annotations

/**
 * @template T
 * @implements \IteratorAggregate<int, T>
 */
final class TypedCollection implements \IteratorAggregate, \Countable
{
    /** @param list<T> $items */
    public function __construct(private array $items = []) {}

    /** @param T $item */
    public function add(mixed $item): void
    {
        $this->items[] = $item;
    }

    /** @return \ArrayIterator<int, T> */
    public function getIterator(): \ArrayIterator
    {
        return new \ArrayIterator($this->items);
    }

    public function count(): int
    {
        return count($this->items);
    }
}

Anti-Patterns / Common Mistakes

Anti-Rationalization Guards

• Do NOT skip declare(strict_types=1) because "it's just a small script" -- add it everywhere.
• Do NOT use mixed without a comment justifying why a narrower type is impossible.
• Do NOT suppress PHPStan errors without a written explanation of why the code is correct.
• Do NOT use the service locator pattern (app()) in business logic, even in Laravel.
• Do NOT skip interfaces for key boundaries because "there's only one implementation" -- there will be two.

Documentation Lookup (Context7)

Use mcp__context7__resolve-library-id then mcp__context7__query-docs for up-to-date docs. Returned docs override memorized knowledge.

• php — for language features, built-in functions, or PHP 8.x syntax
• composer — for package management, autoloading, or scripts configuration

Integration Points

Skill Type

FLEXIBLE — Adapt the process phases to the scope of work. A single function may need only Phase 3 and 4. A new module or package should follow all four phases. Non-negotiable regardless of scope: declare(strict_types=1), PHPStan compliance at the project's configured level, and PSR-4 autoloading.