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Func(T, TResult) Delegate

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

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

type Func = 
    delegate of 
        arg:'T -> 'TResult

Type Parameters

in T

The type of the 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.

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

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.

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.

NoteNote

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.

No code example is currently available or this language may not be supported.

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.

No code example is currently available or this language may not be supported.

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).)


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).)

No code example is currently available or this language may not be supported.

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.

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 method to change the strings in an array of strings to uppercase.

No code example is currently available or this language may not be supported.

.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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