C# Func Type

Func handles many arguments. The Func type is a parameterized type.

We specify the number and kinds of parameters, and the type of the return value. The Func type provides a way to store anonymous methods in a generalized and simple way.

Example. This program uses the lambda expression syntax with Func type instances to store anonymous methods. Each of the Func type instances uses type parameters, and these are specified in the angle brackets < and >.

Lambda

So: The first type parameters are the arguments to the methods, and the final type parameter is the return value.

Generic ClassReturn

C# program that uses Func generic type and lambdas

using System;

class Program
{
    static void Main()
    {
	//
	// Create a Func instance that has one parameter and one return value.
	// ... Parameter is an integer, result value is a string.
	//
	Func<int, string> func1 = (x) => string.Format("string = {0}", x);
	//
	// Func instance with two parameters and one result.
	// ... Receives bool and int, returns string.
	//
	Func<bool, int, string> func2 = (b, x) =>
	    string.Format("string = {0} and {1}", b, x);
	//
	// Func instance that has no parameters and one result value.
	//
	Func<double> func3 = () => Math.PI / 2;

	//
	// Call the Invoke instance method on the anonymous functions.
	//
	Console.WriteLine(func1.Invoke(5));
	Console.WriteLine(func2.Invoke(true, 10));
	Console.WriteLine(func3.Invoke());
    }
}

Output

string = 5
string = True and 10
1.5707963267949

In Main, the program declares and assigns three Func type instances. It uses the full type declaration of the Func types, which includes the parameterized types in the angle brackets.

Note: In the Func types, all of the first parameterized types excluding the last are the argument types.

And: The final parameterized type is the return value. We show two string return values and one double.

The first Func receives an int and returns a string and it is declared as Func<int, string>. The second receives a bool and an int and returns a string. It is declared as Func<bool, int, string>. The third simply returns a value.

IntStringsBool

Finally: This program calls the Invoke method on the Func type instances. Each of the Invoke calls uses different parameters.

Discussion. You cannot call the Invoke method with an invalid number of parameters. The Func type itself stores the required parameter types and uses those to generate the Invoke method signature.

You can use the Func type as a field, return value, local variable, or parameter in your C# programs. You must specify the full type name with the type parameters. In this way we can store delegates by their signatures.

Example: You can add the Func<int, string> as a field, and give it an identifier.

Summary. We looked at the Func parameterized type and used it with the lambda expression syntax. We stored anonymous functions inside Func pointers and then invoked those methods through the Invoke method on the Func instances.

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