Generics and Generic Collections

C# in Visual Studio 2026 — a hands-on guide for developers at every level.

Why Generics?

Generics let you write type-safe, reusable code without knowing the concrete type at compile time. You avoid boxing, casting, and runtime errors.

// Generic stack
public class Stack<T>
{
    private readonly List<T> _items = [];

    public void Push(T item) => _items.Add(item);
    public T Pop()
    {
        if (_items.Count == 0) throw new InvalidOperationException("Empty stack");
        T top = _items[^1];
        _items.RemoveAt(_items.Count - 1);
        return top;
    }
    public int Count => _items.Count;
}

var stack = new Stack<int>();
stack.Push(1); stack.Push(2); stack.Push(3);
Console.WriteLine(stack.Pop()); // 3

Generic Constraints

// T must implement IComparable<T>
static T Max<T>(T a, T b) where T : IComparable<T>
    => a.CompareTo(b) > 0 ? a : b;

Console.WriteLine(Max(3, 7));        // 7
Console.WriteLine(Max("apple", "zebra")); // zebra

Built-in Generic Collections