Generics

Syntax

class ClassName<T> {\n  // T can be used as a type\n}

Examples

public class Box<T>
{
    private T _content = default!;

    public void Set(T content) => _content = content;
    public T Get() => _content;
}

Box<string> stringBox = new Box<string>();
stringBox.Set("Hello");
Console.WriteLine(stringBox.Get());  // Hello

Box<int> intBox = new Box<int>();
intBox.Set(42);
Console.WriteLine(intBox.Get());  // 42

public class Utils
{
    public static void PrintArray<T>(T[] array)
    {
        foreach (T item in array)
        {
            Console.WriteLine(item);
        }
    }
}

int[] numbers = { 1, 2, 3 };
string[] words = { "a", "b", "c" };

Utils.PrintArray(numbers);
Utils.PrintArray(words);

public class Pair<TKey, TValue>
{
    public TKey Key { get; }
    public TValue Value { get; }

    public Pair(TKey key, TValue value)
    {
        Key = key;
        Value = value;
    }

    public override string ToString() => $"{Key} -> {Value}";
}

Pair<string, int> pair = new Pair<string, int>("age", 21);
Console.WriteLine(pair);  // age -> 21

public class NumberBox<T> where T : struct, IComparable<T>
{
    public T Value { get; }
    public NumberBox(T value) => Value = value;

    public bool IsGreaterThan(T other) => Value.CompareTo(other) > 0;
}

NumberBox<int> box = new NumberBox<int>(10);
Console.WriteLine(box.IsGreaterThan(5));  // true

Best practices

• Use generics whenever a class or method's logic is the same regardless of type, to avoid duplicating code for each specific type
• Follow C# naming conventions for type parameters: T for a single general type, TKey/TValue for a key-value pair, TResult for a return type
• Use generic constraints (where T : ...) when your generic code needs to call methods specific to a certain family of types
• Prefer generics over using object and manual casting - generics catch type errors at compile time instead of causing an InvalidCastException at runtime

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation