C# Generics and Collections Explained: Key Concepts for Technical Interviews

Generics and collections are among the most frequently tested topics in C# technical interviews, appearing consistently across junior to senior levels. Before generics, developers had to choose between duplicating classes for each type or using the base object type, both of which carried significant drawbacks including lost type safety and boxing overhead. Generic classes and methods solve this by allowing type parameters to be specified at the point of use, enabling a single implementation to work across multiple types while maintaining compile-time safety. Constraints such as where T : class or where T : IComparable further refine generics by restricting which types are permissible, ensuring required capabilities are available within generic code. A practical example is a generic repository pattern over Entity Framework Core, where a single constrained generic class can handle multiple entity types without redundant implementations.