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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:  mscorlib (in mscorlib.dll)

public delegate TResult Func<in T1, in T2, in T3, out TResult>(
	T1 arg1,
	T2 arg2,
	T3 arg3
)

Type Parameters

in T1

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

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

in T2

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

in T3

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

out TResult

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

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

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 encapsulated 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 instead of 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 (Visual Basic) 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);
   }
}


.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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