Function Delegates in C#: Why They Exist, How They Work, and Where They Shine

You’ve probably used delegates in C#—even if you didn’t realize it. Whenever you use Action, Func, or event, you’re dealing with them.

But what is a delegate, really?
Why did C# invent this feature in the first place?
And how does it power everything from Unity events to LINQ expressions?

Let’s peel it apart from the ground up.

Why Delegates Were Created

Before delegates, C-style languages didn’t have a clean way to treat functions as data. You could call a function, but you couldn’t pass one around easily.

In languages like C, you’d use a function pointer—an address in memory that points to executable code. Powerful, yes—but also dangerous. There was no type safety or protection from calling invalid memory.

C# solved this with delegates: a type-safe, managed wrapper around function pointers.

Delegates give you:

• ✅ Type safety (the compiler checks your method signatures)

• ✅ Garbage collection safety (no dangling pointers)

• ✅ Multicast support (a delegate can call multiple methods in sequence)

• ✅ Full object-oriented integration (delegates are real objects)

So delegates were created to give developers the power of function pointers with the safety of .NET’s type system.

What a Delegate Actually Is

A delegate is like a contract for methods. It defines the shape of a method — what parameters it takes and what it returns.

This means:

“Any method that takes two int parameters and returns an int can be assigned to this delegate.”

Now you can create variables of that type, just like classes:

Just like when you make your own type

And assign methods that match the signature:

operation takes any method that takes 2 ints as parameters and returns an int

Under the hood, operation is an object that knows:

• Which method to call, and

• Which object instance to call it on (for instance methods).

That means delegates let you store, pass, and invoke methods dynamically.

Delegates Are Objects Too

This often surprises people: Delegates aren’t syntactic sugar — they’re actual objects that derive from System.Delegate.

You can even inspect them!

This makes them powerful building blocks for frameworks that need to store or trigger behavior dynamically—like Unity’s event system or ASP.NET request pipelines.

Multicast Delegates

Delegates can point to more than one method at once. These are called multicast delegates.

You can use the += and -= operators to add or remove methods:

Under the hood, Action is just a delegate type that returns void and takes no parameters

Multicast delegates are the foundation for events.

Delegates and Events

Events in C# are built on top of delegates.

Example:

You can think of the question mark after Clicked as a check to ensure it is not null

Now you can subscribe methods to the event:

Multiple methods are subscribed to the event

Output:

Every time you call Click(), all subscribed methods run — thanks to multicast delegate chaining

That’s how UnityEvents, WinForms, WPF, and even ASP.NET MVC middleware work internally.

Delegates in Modern C#: Action, Func, Predicate

C# made delegates easier over time. You almost never write delegate declarations manually anymore.

1. Action

A delegate that returns void.

2. Func

A delegate that returns a value. The last generic type in the Func is the return type.

3. Predicate

A delegate that returns a bool

They’re just shorthand for custom delegate types.

⚡ Anonymous Methods and Lambdas

When C# 2.0 introduced anonymous methods, you could define methods inline without names.

Recall that Actions take no parameters and return nothing (void)

C# 3.0 simplified that into lambda expressions:

A simpler syntax

Under the hood, both compile into delegate objects. That’s why lambdas, LINQ queries, and callbacks all rely on delegates.

Common Use Cases

Delegates are how you “inject behavior” — code that can be passed and executed later

Under the Hood: How Delegates Work

When you assign a method to a delegate:

1. The compiler creates a delegate object.

2. That object stores:

   • A reference to the method (MethodInfo)

   • A reference to the target object (if non-static)

3. When you call the delegate (myDelegate()), it executes that method via Invoke().

You can even call it manually:

That’s literally what the parentheses syntax sugar does

Delegates vs Interfaces

A good mental model:

Delegates vs interfaces

When you only need to pass one behavior (like sorting logic, callbacks, or filters), use a delegate.
When you need a structured type with multiple behaviors, use an interface.

Chaining and Composition

Delegates support chaining, which makes them ideal for pipelines.

That same concept powers LINQ query chains — they’re literally delegate pipelines

Closures: When Delegates Capture Variables

Lambdas can “capture” variables from outer scopes:

Even after the outer scope ends, the delegate keeps a reference to multiplier

This feature is called a closure, and it’s fundamental to functional-style programming in C#.

Real-World Analogy

Think of a delegate as a power socket and your methods as plugs.

• The socket defines a specific shape — that’s the method signature.

• Only plugs (methods) with the right shape fit.

• Once connected, electricity (the delegate invocation) flows and powers the device.

• You can unplug one device and connect another at any time — without changing the socket itself.

• A power strip (multicast delegate) can power multiple devices at once.

That’s exactly what delegates do in code: they provide a safe connection point for interchangeable behaviors — and the compiler ensures the plugs always fit.

That’s why frameworks like Unity, ASP.NET, and MAUI rely on delegates everywhere.

Summary Table

The uses of delegates

Why Delegates Still Matter

Even with async, LINQ, and event-driven frameworks, delegates remain the bridge between object-oriented and functional programming in C#. They make code modular, flexible, and expressive.

Every time you:

• Pass a callback,

• Hook an event,

• Write a lambda,

• Use LINQ,

you’re using delegates — directly or indirectly.

In Short

Delegates let you pass methods like data — safely and cleanly. They’re why C# can blend object-oriented and functional styles so gracefully. Once you understand delegates, you understand how behavior flows through the .NET ecosystem.