What Are Generics in C#?

Technical Definition 

Generics allow developers to create strongly typed components by specifying type parameters that are replaced with actual data types at compile time.

Why Generics Are Needed

Before generics, collections stored data as object, which caused:

• Runtime casting errors
• Boxing and unboxing overhead
• Poor type safety

Generics solve these problems.

Simple Example (Generic Class)

public class MyGeneric<T>
{
    public T Data { get; set; }
}
MyGeneric<int> obj1 = new MyGeneric<int>();
obj1.Data = 100;

MyGeneric<string> obj2 = new MyGeneric<string>();
obj2.Data = "Hello";

• ✔ Compile-time type checking
• ✔ No casting required

Generic Method Example

public void Print<T>(T value)
{
    Console.WriteLine(value);
}
Print<int>(10);
Print<string>("C# Generics");

Generic Collection Example

List<int> numbers = new List<int> { 1, 2, 3 };
List<string> names = new List<string> { "John", "Alex" };

• ✔ Type safe
• ✔ Faster than non-generic collections

Generic Constraints

public class Repository<T> where T : class
{
}

Common Constraints

Constraint	Description
where T : class	Reference type
where T : struct	Value type
where T : new()	Default constructor
where T : BaseClass	Inheritance
where T : interface	Interface implementation

Advantages of Generics

• ✔ Strong type safety
• ✔ Reusable code
• ✔ Better performance
• ✔ Cleaner, maintainable code

One-Line Interview Answer

Generics in C# allow the creation of type-safe and reusable code by defining placeholders for data types that are specified at runtime or compile time.