GRASP (object-oriented design)

GRASP (General Responsibility Assignment Software Patterns) is a set of foundational principles in object-oriented design, aimed at guiding the assignment of responsibilities to classes and objects to create maintainable, understandable, and reusable software. These principles are not strict rules, but rather patterns that suggest how to distribute responsibilities effectively. GRASP helps developers make informed decisions about which class should handle which task, leading to a more robust and flexible design.

The GRASP patterns include the following:

• Information Expert: Assigns responsibility to the class that has the information needed to fulfill it. This often minimizes dependencies and promotes encapsulation.

• Creator: Focuses on who should be responsible for creating instances of a class. The guideline suggests assigning creation responsibility to a class that either contains, uses closely, records, or aggregates instances of the class being created, or has the initializing data.

• High Cohesion: Aims to keep related responsibilities together within a single class. High cohesion leads to focused classes that are easier to understand, maintain, and reuse.

• Low Coupling: Seeks to minimize the dependencies between classes. Low coupling results in a design where changes in one class are less likely to impact other parts of the system. This increases flexibility and reduces the risk of cascading changes.

• Controller: Determines which class should handle system events or user interface input. It typically delegates the actual work to other classes.

• Polymorphism: Encourages the use of polymorphic operations to handle variations in behavior. This promotes flexibility and extensibility by allowing different classes to implement the same interface or inherit from a common base class.

• Pure Fabrication: Suggests creating an artificial class that does not represent a domain concept but is solely created to support high cohesion and low coupling when responsibilities don't naturally fit within existing classes. These are often service or utility classes.

• Indirection: Introduces an intermediary object to decouple two classes that would otherwise be directly coupled. This can improve reusability and adaptability, especially when direct interaction is undesirable or complex.

• Protected Variations: Aims to protect elements of a system from the variations of other elements by encapsulating the point of variation behind an interface. This pattern anticipates change and insulates the system from its impact.

Applying GRASP principles is an iterative process during object-oriented analysis and design. Developers may need to consider multiple patterns and weigh their trade-offs to find the best solution for a given problem. The goal is to achieve a balance between cohesion, coupling, and other design considerations to create a maintainable and effective software system.