Encapsulates a method that has one parameter and returns a value of the type specified by the TResult parameter.

To browse the .NET Framework source code for this type, see the Reference Source.

Namespace:   System Assembly:  mscorlib (in mscorlib.dll)

Syntax

C#

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

Parameters

arg

Type: T

The parameter of the method that this delegate encapsulates.

Return Value

Type: TResult

The return value of the method that this delegate encapsulates.

Type Parameters

in T

The type of the parameter of the method that this delegate encapsulates.

out TResult

The type of the return value of the method that this delegate encapsulates.

Remarks

Note

To view the .NET Framework source code for this type, see the Reference Source. You can browse through the source code online, download the reference for offline viewing, and step through the sources (including patches and updates) during debugging; see instructions.

You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have one parameter that is passed to it by value, and that it must return a value.

Note

To reference a method that has one parameter and returns void (or in Visual Basic, that is declared as a Sub rather than as a Function), use the generic Action<T> delegate instead.

When you use the Func<T, TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with a single parameter. For example, the following code explicitly declares a delegate named ConvertMethod and assigns a reference to the UppercaseString method to its delegate instance.

C#

using System; delegate string ConvertMethod(string inString); public class DelegateExample{   public static void Main()   {      // Instantiate delegate to reference UppercaseString method      ConvertMethod convertMeth = UppercaseString;      string name = "Dakota";      // Use delegate instance to call UppercaseString method      Console.WriteLine(convertMeth(name));   }    private static string UppercaseString(string inputString)   {      return inputString.ToUpper();   }}

The following example simplifies this code by instantiating the Func<T, TResult> delegate instead of explicitly defining a new delegate and assigning a named method to it.

C#

using System; public class GenericFunc{   public static void Main()   {      // Instantiate delegate to reference UppercaseString method      Func<string, string> convertMethod = UppercaseString;      string name = "Dakota";      // Use delegate instance to call UppercaseString method      Console.WriteLine(convertMethod(name));   }    private static string UppercaseString(string inputString)   {      return inputString.ToUpper();   }}

You can also use the Func<T, TResult> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods (C# Programming Guide).)

C#

using System; public class Anonymous{   public static void Main()   {      Func<string, string> convert = delegate(string s)         { return s.ToUpper();};        string name = "Dakota";      Console.WriteLine(convert(name));      }}

You can also assign a lambda expression to a Func<T, TResult> delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (Visual Basic) and Lambda Expressions (C# Programming Guide).)

C#

using System; public class LambdaExpression{   public static void Main()   {      Func<string, string> convert = s => s.ToUpper();       string name = "Dakota";      Console.WriteLine(convert(name));      }}

The underlying type of a lambda expression is one of the generic Func delegates. This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. In particular, because many methods of types in the System.Linq namespace have Func<T, TResult> parameters, you can pass these methods a lambda expression without explicitly instantiating a Func<T, TResult> delegate.

Examples

The following example demonstrates how to declare and use a Func<T, TResult> delegate. This example declares a Func<T, TResult> variable and assigns it a lambda expression that converts the characters in a string to uppercase. The delegate that encapsulates this method is subsequently passed to the Enumerable.Select<TSource, TResult> method to change the strings in an array of strings to uppercase.

C#

using System;using System.Collections;using System.Collections.Generic;using System.Linq; static class Func{   static void Main(string[] args)   {      // Declare a Func variable and assign a lambda expression to the        // variable. The method takes a string and converts it to uppercase.      Func<string, string> selector = str => str.ToUpper();       // Create an array of strings.      string[] words = { "orange", "apple", "Article", "elephant" };      // Query the array and select strings according to the selector method.      IEnumerable<String> aWords = words.Select(selector);       // Output the results to the console.      foreach (String word in aWords)         Console.WriteLine(word);   }}      /*This code example produces the following output:    ORANGE   APPLE   ARTICLE   ELEPHANT*/