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Lesson 3318 min read

Generics

Learn how to write type-safe, reusable classes and methods using C# generics.

C# & .NET learning pathLesson 33 of 66
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The Problem Generics Solve

Without generics, you'd need a separate method or class for every type you want to support (PrintInt, PrintString, PrintBool...). Generics let you write one implementation that works with any type, safely.

You've Already Used Generics

List<T> and Dictionary<TKey, TValue> from the previous lesson are themselves generic types — the <T> syntax lets them work with any type you plug in.

Generic Methods

static void Print<T>(T value)
{
    Console.WriteLine($"Value: {value}");
}


Print(42);       // T is int
Print("hello");  // T is string
Print(3.14);     // T is double

Generic Classes

class Box<T>
{
    private T content;


    public void Store(T item) => content = item;
    public T Retrieve() => content;
}


var intBox = new Box<int>();
intBox.Store(42);
Console.WriteLine(intBox.Retrieve());


var stringBox = new Box<string>();
stringBox.Store("Hello");
Console.WriteLine(stringBox.Retrieve());
Output

Click Run to see what this code prints.

Type Constraints

You can restrict which types are allowed with the where clause — useful when your generic code needs to call specific members on the type.

static T Max<T>(T a, T b) where T : IComparable<T>
{
    return a.CompareTo(b) > 0 ? a : b;
}


Console.WriteLine(Max(5, 10));      // 10
Console.WriteLine(Max("apple", "banana")); // banana

FAQs

No — the CLR specializes generic code for value types at compile/JIT time, so there's effectively no performance penalty.

Summary

  • Generics let you write one implementation that works across many types safely.
  • List<T> and Dictionary<TKey,TValue> are built-in generic types.
  • Type constraints (where) restrict which types are allowed and what you can do with them.
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Delegates