It means that you should put new code in new classes/modules. Existing code should be modified only for bug fixing. New classes can reuse existing code via inheritance. Open/closed principle is intended to mitigate risk when introducing new functionality. Since you don’t modify existing code you can be assured that it wouldn’t be broken. It …
I’ve taken a class in college that spent two weeks around design patters, and read the Gang of Four book to no avail. Understanding what each pattern served for and how to use them to fit my problems was very hard for me, a developer that didn’t have much experience in OO programming. The book …
Rich Domain Model (RDM) and Single Responsibility Principle (SRP) are not necessarily at odds. RDM is more at odds with a very specialised subclassof SRP – the model advocating “data beans + all business logic in controller classes” (DBABLICC). If you read Martin’s SRP chapter, you’ll see his modem example is entirely in the domain …
Design is the management and balance of trade-offs. YAGNI and SOLID aren’t conflicting: the former says when to add features, the latter says how, but they both guide the design process. My responses, below, to each of your specific quotes use principles from both YAGNI and SOLID. It is three times as difficult to build …
Subclasses overriding methods in the base class are totally allowed by the Liskov Substituion Principle. This might be simplifying it too much, but I remember it as “a subclass should require nothing more and promise nothing less” If a client is using a superclass ABC with a method something(int i), then the client should be …
SRP tells us that you should only have a single responsibility in a module. ISP tells us that you should not be forced to be confronted with more than you actually need. If you want to use a print() method from interface I, you shouldn’t have to instantiate a SwimmingPool or a DriveThru class for …
This is easy once you realize that Object-Oriented Constructor Injection corresponds very closely to Functional Partial Function Application. First, I’d write Dings as a record type: type Dings = { Lol : string; Rofl : string } In F#, the IGetStuff interface can be reduced to a single function with the signature Guid -> seq<Dings> …
(This answer has been rewritten 2013-05-13, read the discussion in the bottom of the comments) LSP is about following the contract of the base class. You can for instance not throw new exceptions in the sub classes as the one using the base class would not expect that. Same goes for if the base class …
Single Responsibility Principle (SRP)- give each class just one reason to change; and “Reason to change” == “responsibility”. In example: Invoice class does not have a responsibility to print itself. Separation of Concerns (since 1974). Concern == feature of system. Taking care of each of the concerns: for each one concern, other concerns are irrelevant. …
What Is It? The books Agile Software Development, Principles, Patterns, and Practices and Agile Principles, Patterns, and Practices in C# are the best resources for fully understanding the original goals and motivations behind the Dependency Inversion Principle. The article “The Dependency Inversion Principle” is also a good resource, but due to the fact that it …