C# Collections and Generics

Generic Collections

C# generics let collections work with any type while staying type-safe. The main ones live in System.Collections.Generic.

List<T>

var names = new List<string> { "Sara", "Ali" };
names.Add("Omar");
names[0]; // "Sara"

Dictionary<K,V>

var ages = new Dictionary<string, int>();
ages["Sara"] = 25;
ages.TryGetValue("Sara", out int age); // safe lookup

HashSet<T>

var unique = new HashSet<int> { 1, 2, 2, 3 }; // {1,2,3}

Writing a Generic Method

T First<T>(List<T> items) => items[0];
int n = First(new List<int> { 1, 2 });  // type inferred

FAQs

List vs Array?

Arrays are fixed-size; List grows dynamically. Prefer List for most cases. More in our C# guides.

Why generics over object?

Type safety and no boxing/casting overhead.