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Func<T1, T2, T3, TResult> Delegate

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

Namespace:  System
Assembly:  System.Core (in System.Core.dll)
public delegate TResult Func<T1, T2, T3, TResult>(
	T1 arg1,
	T2 arg2,
	T3 arg3
)

Type Parameters

T1

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

T2

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

T3

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

TResult

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

Parameters

arg1
Type: T1

The first parameter of the method that this delegate encapsulates.

arg2
Type: T2

The second parameter of the method that this delegate encapsulates.

arg3
Type: T3

The third parameter of the method that this delegate encapsulates.

Return Value

Type: TResult
The return value of the method that this delegate encapsulates.

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

NoteNote:

To reference a method that has three parameters and returns void (or in Visual Basic, that is declared as a Sub rather than as a Function), use the generic Action<T1, T2, T3> delegate instead.

When you use the Func<T1, T2, T3, TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with three parameters. For example, the following code explicitly declares a generic delegate named ParseNumber and assigns a reference to the Parse method to its delegate instance.

using System;
using System.Globalization;

delegate T ParseNumber<T>(string input, NumberStyles styles, 
                         IFormatProvider provider);

public class DelegateExample
{
   public static void Main()
   {
      string numericString = "-1,234";
      ParseNumber<int> parser = int.Parse;
      Console.WriteLine(parser(numericString, 
                        NumberStyles.Integer | NumberStyles.AllowThousands, 
                        CultureInfo.InvariantCulture));
   }
}

The following example simplifies this code by instantiating the Func<T1, T2, T3, TResult> delegate rather than explicitly defining a new delegate and assigning a named method to it.

using System;
using System.Globalization;

public class GenericFunc
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser = int.Parse;
      Console.WriteLine(parser(numericString, 
                        NumberStyles.Integer | NumberStyles.AllowThousands, 
                        CultureInfo.InvariantCulture));
   }
}

You can use the Func<T1, T2, T3, TResult> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods (C# Programming Guide).)

using System;
using System.Globalization;

public class Anonymous
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser = 
           delegate(string s, NumberStyles sty, IFormatProvider p) 
           { return int.Parse(s, sty, p); };
      Console.WriteLine(parser(numericString, 
                        NumberStyles.Integer | NumberStyles.AllowThousands, 
                        CultureInfo.InvariantCulture));
   }
}

You can also assign a lambda expression to a Func<T1, T2, T3, TResult> delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions and Lambda Expressions (C# Programming Guide).)

using System;
using System.Globalization;

public class LambdaExpression
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser = (s, sty, p)
                   => int.Parse(s, sty, p);
      Console.WriteLine(parser(numericString, 
                        NumberStyles.Integer | NumberStyles.AllowThousands, 
                        CultureInfo.InvariantCulture));
   }
}

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 parameters, you can pass these methods a lambda expression without explicitly instantiating a Func delegate.

The following example demonstrates how to declare and use a Func<T1, T2, TResult> delegate. This example declares a Func<T1, T2, TResult> variable and assigns it a lambda expression that takes a String value and an Int32 value as parameters. The lambda expression returns true if the length of the String parameter is equal to the value of the Int32 parameter. The delegate that encapsulates this method is subsequently used in a query to filter strings in an array of strings.

using System;
using System.Collections.Generic;
using System.Linq;

public class Func3Example
{
   public static void Main()
   {
      Func<String, int, bool> predicate = (str, index) => str.Length == index;

      String[] words = { "orange", "apple", "Article", "elephant", "star", "and" };
      IEnumerable<String> aWords = words.Where(predicate).Select(str => str);

      foreach (String word in aWords)
         Console.WriteLine(word);
   }
}

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0
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