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What are generics and why use them? How do you declare a generic class with a type parameter, and how do you instantiate it with a specific type? What are generic constraints and why are they needed? What is covariance and contravariance in generics? Why can't you use operators like + directly on an unconstrained generic T? How do generic type constraints ('where T : ...') restrict what types can be used, and what are the common constraint kinds? How does generic type inference work when calling a generic method, and when do you need to specify the type argument explicitly? What is covariance ('out T') and contravariance ('in T') in generic interfaces, and how does IEnumerable<out T> demonstrate covariance? What are generics in C#, and what specific problems do they solve compared to writing type-specific code? How are generics implemented for value types vs reference types in the CLR?
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What problem do generics solve compared to writing a method or class that accepts 'object'?

Beginner

Answer

Using 'object' loses type safety entirely — you'd need to cast every value back to its real type manually, risking runtime InvalidCastExceptions, and value types get boxed. Generics let a class or method work with MULTIPLE specific types while the compiler enforces type safety and avoids unnecessary boxing, checked entirely at compile time.
// Using object: loses type safety, requires casting, boxes value types
public object GetFirst(object[] items) => items[0];

// Using generics: fully type-safe, no casting, no boxing for value types
public T GetFirst<T>(T[] items) => items[0];
int first = GetFirst(new int[] { 1, 2, 3 }); // no cast needed, no boxing
Real-world example Writing a single, reusable Stack<T> or Repository<T> class that works safely and efficiently with any specific type.

Common follow-ups: Why specifically does using 'object' for value types cause boxing, and why is that a performance concern?

Structs Boxing & Unboxing
All 17 Generics questions