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version: "1.0.1" name: grasp-knowledge description: GRASP principles knowledge base for PHP 8.4 projects. Provides quick reference for 9 responsibility assignment patterns (Information Expert, Creator, Controller, Low Coupling, High Cohesion, Polymorphism, Pure Fabrication, Indirection, Protected Variations). Use for architecture audits and design decisions.
GRASP Principles Knowledge Base
Overview
GRASP (General Responsibility Assignment Software Patterns) provides guidelines for assigning responsibilities to classes and objects in object-oriented design.
| Principle | Core Question | Goal | |
|---|---|---|---|
| Information Expert | Who has the data? | Assign to class with information | |
| Creator | Who creates objects? | Assign creation responsibility | |
| Controller | Who handles system events? | Coordinate use case flow | |
| Low Coupling | How to reduce dependencies? | Minimize interconnections | |
| High Cohesion | How to focus responsibilities? | Keep related things together | |
| Polymorphism | How to handle type variations? | Use polymorphic operations | |
| Pure Fabrication | What if no domain class fits? | Create artificial class | |
| Indirection | How to decouple? | Add intermediate object | |
| Protected Variations | How to handle change? | Hide variation points |
Quick Detection Patterns
Information Expert Violations
# Feature Envy: Class uses other class's data moreGrep: "->get.*->get.*->get" --glob "**/*.php"# Train wreck callsGrep: "->.*()->.*()->.*()->" --glob "**/*.php"
Signs: Method accesses other object's data extensively, data and behavior separated.
Creator Violations
# Random creation locationsGrep: "new\s\+[A-Z][a-z]*[A-Z]" --glob "**/*.php"
Signs: Objects created in unexpected places, no clear creation ownership.
Controller Violations
# Fat controllers (>100 lines)find . -path "*/Controller/*.php" -exec wc -l {} \; | awk '$1 > 100'# Business logic in controllersGrep: "if.*&&.*||" --glob "*Controller.php"
Signs: Controller has >100 lines, business logic in controller.
Low Coupling Violations
# High dependency count (>7)Grep: "__construct" --glob "**/*.php" -A 15# Concrete type dependenciesGrep: "function.*([A-Z][a-z]*[A-Z]" --glob "**/*.php"
Signs: Class has >7 dependencies, depends on concrete classes.
High Cohesion Violations
# Unrelated method namesGrep: "public function" --glob "**/*.php" | grep -E "And[A-Z]|Or[A-Z]"# Multiple responsibilities in class nameGrep: "class.*Manager|class.*Handler|class.*Processor" --glob "**/*.php"
Signs: Methods don't relate to each other, class does many unrelated things.
Quick PHP 8.4 Examples
Information Expert
// BAD: Logic outside of object with datafinal class OrderService{public function calculateTotal(Order $order): Money{$total = Money::zero();foreach ($order->getLines() as $line) {$total = $total->add($line->getProduct()->getPrice()->multiply($line->getQuantity()));}return $total;}}// GOOD: Logic in class that has the datafinal class Order{public function total(): Money{return array_reduce($this->lines,fn(Money $sum, OrderLine $line) => $sum->add($line->total()),Money::zero(),);}}
Low Coupling
// BAD: Depends on concrete classesfinal class ReportGenerator{public function __construct(private DoctrineOrderRepository $orders,private SymfonyMailer $mailer,) {}}// GOOD: Depends on abstractionsfinal readonly class ReportGenerator{public function __construct(private OrderReader $orders,private Mailer $mailer,) {}}
High Cohesion
// BAD: Low cohesion - unrelated responsibilitiesfinal class UserManager{public function register(array $data): User { }public function sendEmail(User $user): void { }public function generateReport(): string { }}// GOOD: High cohesion - focused responsibilitiesfinal readonly class UserRegistrationService{public function register(RegistrationData $data): User { }public function confirmEmail(Token $token): void { }}
GRASP & DDD Integration
| GRASP | DDD Application | |
|---|---|---|
| Information Expert | Entities contain their behavior | |
| Creator | Aggregates create their entities | |
| Controller | Application Services / Use Cases | |
| Low Coupling | Bounded Context boundaries | |
| High Cohesion | Aggregate consistency boundary | |
| Polymorphism | Domain Services, Strategies | |
| Pure Fabrication | Repositories, Factories, Specifications | |
| Indirection | Anti-Corruption Layer, Adapters | |
| Protected Variations | Ports & Adapters, Domain Events |
References
For detailed patterns and examples, see references/:
information-expert.md— Tell Don't Ask, calculations in ownercreator.md— Factory patterns, aggregation rulescontroller.md— Use case handlers, thin controllerslow-coupling.md— Dependency injection, abstractionshigh-cohesion.md— Focused responsibilitiespolymorphism.md— Strategy pattern, type variationspure-fabrication.md— Repositories, specificationsindirection.md— Adapters, mediatorsprotected-variations.md— Stable interfacesantipatterns.md— Common GRASP violations
Assets
assets/report-template.md— GRASP audit report format