Func, Action And Predicate Delegates In C#

Introduction

We learned what delegates are in this article.

Whenever we use delegates, we have to declare a delegate then initialize it, then we call a method with a reference variable.

In order to get rid of all the first steps, we can directly use Func, Action, or Predicate delegates.

The Func delegate takes zero, one or more input parameters, and returns a value (with its out parameter).
Action takes zero, one or more input parameters, but does not return anything.
Predicate is a special kind of Func. It represents a method that contains a set of criteria mostly defined inside an if condition and checks whether the passed parameter meets those criteria or not.

It takes one input parameter and returns a boolean - true or false.

Note

You can use all three of them with anonymous methods and lambda expressions.

Let's first learn the Func delegate.

Syntax 1

One input parameter and one return parameter.

public delegate TResult Func<int T, out TResult>(T arg);

Syntax 2

Two input parameters and one return parameter.

public delegate TResult Func<in T1, in T2, out TResult>(T1 arg, T2 arg2)

The last parameter in the angle brackets <> is considered as the return type and remaining parameters are considered as input parameter types.

It can have 0 - 16 input parameters.

Func with 0 parameters

Func<int> SomeMethodName;

It still has one parameter, it is a return type because func always return something.

class Program  
   {  
 static void Main(string[] args)  
       {  
           Func<int, int, int> Addition = AddNumbers;  
 int result = Addition(10, 20);  
           Console.WriteLine($"Addition = {result}");  
       }  
 
 private static int AddNumbers(int param1, int param2 )  
       {  
 return param1 + param2;  
       }          

  }

Func with an Anonymous Method:

Func< int, int, int > Addition = delegate (int param1, int param2)    
{    
 return param1 + param2;    
};    
int result = Addition(10, 20);    
Console.WriteLine($"Addition = {result}");

Func with Lambda Expression:

Func<int, int, int> Addition = (param1, param2) => param1 + param2;  
 int result = Addition(10, 20);  
            Console.WriteLine($"Addition = {result}");

Action delegate

Here, method AddNumbers takes 2 parameters but returns nothing. The results are assigned to an instance variable result.

Even an ion delegate can have 0 - 16 input parameters.

private static int result;  
 static void Main(string[] args)  
        {  
            Action<int, int> Addition = AddNumbers;  
            Addition(10, 20);  
            Console.WriteLine($"Addition = {result}");  
        }  
 
 private static void AddNumbers(int param1, int param2 )  
        {  
            result = param1 + param2;  
        }

Action with an Anonymous method:

private static int result;  
 static void Main(string[] args)  
       {  
           Action<int, int> Addition = delegate (int param1, int param2)  
           {  
               result = param1 + param2;  
           };  
           Addition(10, 20);  
           Console.WriteLine($"Addition = {result}");  
       }

Action with a Lambda expression:

private static int result;  
 static void Main(string[] args)  
       {  
           Action<int, int> Addition  = (param1, param2) => result = param1 + param2; ;  
           Addition(10, 20);  
           Console.WriteLine($"Addition = {result}");  
       }

Predicate delegate

Syntax difference between predicate & func is that here in predicate, you don't specify a return type because it is always a bool.

Let's check if the phone is an iPhone or not...

class Program  
{  
 static void Main(string[] args)  
    {  
        Predicate<string> CheckIfApple = IsApple;  
 bool result  = IsApple("I Phone X");  
 if(result)  
        Console.WriteLine("It's an IPhone");  
    }  
 
 private static bool IsApple(string modelName)  
    {  
 if (modelName == "I Phone X")  
 return true;  
 else 
 return false;  
    }  
}

A predicate with Anonymous method:

Predicate < string > CheckIfApple = delegate(string modelName) {  
 if (modelName == "I Phone X") return true;  
 else return false;  
};  
bool result = CheckIfApple("I Phone X");  
if (result) Console.WriteLine("It's an IPhone");

A predicate with Lambda expressions:

Predicate < string > CheckIfApple = modelName => { 
if (modelName == "I Phone X") return true;  
 else return false;  
};  
bool result = CheckIfApple("I Phone X");  
if (result) Console.WriteLine("It's an IPhone");

Wonderful!

That's how you can directly use ready-made delegates without having them declared.

I hope this blog has given you the basic idea of delegate types. Be sure to implement them in your project.

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