Understanding Delegates in .NET Core: Types, Scenarios, Pros & Cons

Delegates are one of the core building blocks of the .NET platform. They provide flexibility, extensibility, and type safety in application design. In this article, we’ll explore what delegates are, their types, where to use them, and their advantages and disadvantages in .NET Core applications.

What is a Delegate?

A delegate in .NET is a type that encapsulates a reference to a method. Think of it as a type-safe function pointer. Delegates are widely used for callbacks, event handling, and functional programming.

Example:

public delegate int Calculate(int x, int y);

public class MathOperations {
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
}

// Usage
MathOperations math = new MathOperations();
Calculate calc = new Calculate(math.Add);
int result = calc(5, 3); // Output: 8

Types of Delegates in .NET Core

1. Single-cast Delegate

Action sayHello = () => Console.WriteLine("Hello!");
sayHello();

2. Multi-cast Delegate

void Method1() => Console.WriteLine("Method 1");
void Method2() => Console.WriteLine("Method 2");

Action greet = Method1;
greet += Method2;
greet(); // Invokes both methods

3. Func<> Delegate

Func<int, int, int> add = (x, y) => x + y;
Console.WriteLine(add(3, 4));

4. Action<> Delegate

Action<string> print = msg => Console.WriteLine(msg);
print("Hello World");

5. Predicate<> Delegate

Predicate<int> isEven = x => x % 2 == 0;
Console.WriteLine(isEven(10)); // True

Common Use Cases for Delegates

• Event Handling: Core to Windows Forms, WPF, and custom events
• Callbacks: For async programming and background operations
• LINQ: Filtering, projection, aggregation (uses Func, Predicate)
• Strategy Pattern: Swap behaviors at runtime
• ASP.NET Core Middleware: RequestDelegate to process HTTP requests

Pros of Delegates

• ✅ Type-Safe: Compile-time method signature checking
• ✅ Flexible: Assign or change methods dynamically
• ✅ Multicast Support: Call multiple methods with one delegate
• ✅ Decoupled Design: Promotes low coupling between components

Cons of Delegates

• ⚠️ Harder to Debug: Especially with multi-cast delegates
• ⚠️ Memory Leaks: If event handlers aren’t properly unsubscribed
• ⚠️ Readability: Overuse can lead to unclear code
• ⚠️ Slight Overhead: Slightly slower than direct method calls

⚠️ Watch out: Always unsubscribe from events (especially in long-lived classes) to avoid memory leaks!

Real-World Uses in .NET Core

Scenario	Use of Delegate
ASP.NET Core Middleware	RequestDelegate to process requests
Event-Driven Architecture	Delegates define and invoke custom events
Strategy Pattern	Swap logic dynamically using Func/Action
Background Jobs	Configure retry logic with callbacks
LINQ Queries	Built-in delegates like Func, Predicate

Conclusion

Delegates are powerful tools for building clean, extensible, and decoupled architectures in .NET Core. They’re essential in event-driven systems, middleware pipelines, and functional patterns. Use them where flexibility is needed — but avoid overuse in large, public-facing APIs where clarity matters most.