grasp-responsibility-design

name	grasp-responsibility-design
description	Assigns object responsibilities with GRASP. Use when deciding which object should create, know, coordinate, vary, mediate, or protect behavior in an object-oriented design.

GRASP Responsibility Design

Overview

GRASP patterns are decision tools for assigning responsibilities. Use them to keep behavior near the right information while controlling coupling, cohesion, and variation.

When to Use

• You have use cases, SSDs, contracts, or domain concepts and need software object responsibilities.
• Multiple classes could plausibly perform the same behavior.
• Creation, coordination, variation, or dependency pressure is unclear.
• Do not use as a naming exercise after responsibilities have already been chosen.

Language Adaptation

When the implementation language is known, also use Software Design Language Adaptation and read only its matching language reference. Preserve the GRASP rationale while allowing a responsibility owner to become a native type, function, module, callable, or other appropriate construct rather than forcing a class.

Workflow

1. Start from a responsibility. Phrase it as "Who should know..." or "Who should do..."
2. Try Information Expert first. Assign behavior to the class with the information needed to fulfill it.
3. Apply Creator for object creation. Prefer a creator that contains, aggregates, records, closely uses, or has initialization data for the created object.
4. Choose a Controller for system events. Use a facade controller for system-wide events or a use-case/session controller for scenario coordination.
5. Check Low Coupling. Reject assignments that create unnecessary dependency chains or knowledge of unstable details.
6. Check High Cohesion. Reject assignments that overload an object with unrelated work.
7. Use Polymorphism for type-varying behavior. Put alternatives behind a common interface rather than branching on type.
8. Use Pure Fabrication when domain objects would become bloated or coupled. Create a service-like object only to preserve cohesion and reuse.
9. Use Indirection to mediate dependencies. Insert an intermediate object when direct coupling creates design pressure.
10. Use Protected Variations. Identify likely variation points and stabilize access through interfaces or adapters.

Decision Record Template

## Responsibility Decision: [responsibility]

Candidates:
- [Class]: [reason for/against]

Chosen Owner: [Class]
GRASP Basis: [Expert / Creator / Controller / etc.]
Coupling/Cohesion Check: [impact]
Variation Point: [none or protected by interface/polymorphism]

Red Flags

• A controller performs business rules instead of coordinating.
• A domain object knows about UI, persistence, infrastructure, or external APIs.
• Type checks replace polymorphic dispatch for stable variants.
• "Service" or "Manager" is chosen before evaluating Expert, Creator, and Controller.

Verification

• Each non-trivial behavior has an explicit owner.
• Responsibility decisions cite at least one GRASP rationale.
• Controllers coordinate but do not absorb domain logic.
• Coupling and cohesion were checked for each major assignment.
• Variation points are protected by polymorphism, interfaces, adapters, or indirection.