grasp-knowledge

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 more
Grep: "->get.*->get.*->get" --glob "**/*.php"

# Train wreck calls
Grep: "->.*()->.*()->.*()->" --glob "**/*.php"

Signs: Method accesses other object's data extensively, data and behavior separated.

Creator Violations

# Random creation locations
Grep: "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 controllers
Grep: "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 dependencies
Grep: "function.*([A-Z][a-z]*[A-Z]" --glob "**/*.php"

Signs: Class has >7 dependencies, depends on concrete classes.

High Cohesion Violations

# Unrelated method names
Grep: "public function" --glob "**/*.php" | grep -E "And[A-Z]|Or[A-Z]"

# Multiple responsibilities in class name
Grep: "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 data
final 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 data
final 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 classes
final class ReportGenerator
{
    public function __construct(
        private DoctrineOrderRepository $orders,
        private SymfonyMailer $mailer,
    ) {}
}

// GOOD: Depends on abstractions
final readonly class ReportGenerator
{
    public function __construct(
        private OrderReader $orders,
        private Mailer $mailer,
    ) {}
}

High Cohesion

// BAD: Low cohesion - unrelated responsibilities
final class UserManager
{
    public function register(array $data): User { }
    public function sendEmail(User $user): void { }
    public function generateReport(): string { }
}

// GOOD: High cohesion - focused responsibilities
final 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 owner
• creator.md — Factory patterns, aggregation rules
• controller.md — Use case handlers, thin controllers
• low-coupling.md — Dependency injection, abstractions
• high-cohesion.md — Focused responsibilities
• polymorphism.md — Strategy pattern, type variations
• pure-fabrication.md — Repositories, specifications
• indirection.md — Adapters, mediators
• protected-variations.md — Stable interfaces
• antipatterns.md — Common GRASP violations

Assets

• assets/report-template.md — GRASP audit report format