SOLID Design in C#: The Open-Close Principle (OCP)

A practical guide to the Open-Closed Principle (OCP), the 'O' in SOLID, applied to C# and .NET. Covers the core idea that modules should be open for extension but closed for modification, illustrated with a shape-drawing example that evolves from type-checking if/else chains to an IShape interface abstraction. Also explores the Point of Variation principle as a more actionable framing, discusses the tension between OCP and YAGNI/KISS, and extends the example to the Visitor pattern for handling double dispatch when both shapes and algorithms need to vary independently. Includes practical tips on detecting OCP violations via downcasting, is/as operators, and static analysis tools like NDepend.