0Pricing
C# Academy · Lesson

delegate, Action/Func, closures

Pass behavior via delegates: declare custom delegates, use built-in Action/Func, and see how lambdas capture variables (closures).

delegate, Action/Func, closures is a free C# Academy lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Delegates overview

Goal: Treat methods as data.

  • Define a delegate type
  • Use Action/Func
  • Create lambdas
  • Understand closures (captured variables)

Custom delegate basics

A delegate is a type-safe function pointer. Assign compatible methods and invoke like a function.

using System;

// Custom delegate type: a method taking two ints and returning int
public delegate int Op(int x, int y);

public class Program
{
  static int Add(int a, int b) { return a + b; }
  static int Mul(int a, int b) { return a * b; }

  public static void Main(string[] args)
  {
    Op f = Add;                // method group conversion
    Console.WriteLine(f(2, 3)); // 5
    f = Mul;
    Console.WriteLine(f(2, 3)); // 6
  }
}

Action & Func

Action represents void-returning methods; Func returns a value. Use method groups or lambdas.

using System;

public class Program
{
  static void Log(string s) { Console.WriteLine("LOG: " + s); }

  public static void Main(string[] args)
  {
    Action<string> a = Log;                        // no return
    a("hello");

    Func<int, int, int> sum = delegate(int x, int y) { return x + y; }; // lambda/anon method
    Console.WriteLine(sum(3, 4)); // 7

    // Method group to Func
    Func<string, int> len = GetLen;
    Console.WriteLine(len("abc")); // 3
  }

  static int GetLen(string s) { return s == null ? 0 : s.Length; }
}

Closure demo

A closure captures variables from the outer scope. The variable outlives the method that created the delegate.

using System;

public class Program
{
  public static void Main(string[] args)
  {
    int counter = 0; // captured variable (lives as long as delegate)
    Action inc = delegate() { counter = counter + 1; Console.WriteLine(counter); };

    inc(); // 1
    inc(); // 2
    Console.WriteLine("Final=" + counter); // 2
  }
}

Higher-order method

Pass a Func or Action to customize behavior. This is the basis for many APIs (and LINQ).

using System;

public class Program
{
  // Apply a transform to each number and sum the results
  static int SumBy(int[] xs, Func<int, int> transform)
  {
    int total = 0;
    for (int i = 0; i < xs.Length; i++)
    {
      total += transform(xs[i]);
    }
    return total;
  }

  public static void Main(string[] args)
  {
    int[] data = new int[] { 1, 2, 3 };
    int sumSquares = SumBy(data, delegate(int x) { return x * x; });
    Console.WriteLine(sumSquares); // 14
  }
}

Delegate tips

Tips:

  • Prefer Action/Func to avoid extra custom delegate types.
  • Keep lambdas short and clear.
  • Be mindful of captured variables; their value can change later.
  • Use method groups when a named method already matches the signature.

Func vs Action meaning

Quick check: Which built-in delegate type represents a method that returns a value?

Recap

Recap: Declare delegates, use Action/Func, and write small lambdas. Closures let lambdas capture local variables—use carefully.

Frequently asked questions

Is the “delegate, Action/Func, closures” lesson free?

Yes — the full text of “delegate, Action/Func, closures” is free to read here on the web, and the C# Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO.

What will I learn in “delegate, Action/Func, closures”?

Pass behavior via delegates: declare custom delegates, use built-in Action/Func, and see how lambdas capture variables (closures). You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C# Academy?

No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “delegate, Action/Func, closures” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C# Academy lesson?

Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. delegate, Action/Func, closures
  2. Events: publish/subscribe, event keyword
  3. Event patterns, pitfalls (memory leaks)
← Back to C# Academy