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Func`1.xml
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<Type Name="Func<TResult>" FullName="System.Func<TResult>">
<TypeSignature Language="C#" Value="public delegate TResult Func<out TResult>();" FrameworkAlternate="dotnet-uwp-10.0;net-5.0;net-6.0;net-7.0;net-8.0;net-9.0;netcore-1.0;netcore-1.1;netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0;netcore-3.1;netframework-4.0;netframework-4.5;netframework-4.5.1;netframework-4.5.2;netframework-4.6;netframework-4.6.1;netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1;netstandard-1.0;netstandard-1.1;netstandard-1.2;netstandard-1.3;netstandard-1.4;netstandard-1.5;netstandard-1.6;netstandard-2.0;netstandard-2.1" />
<TypeSignature Language="ILAsm" Value=".class public auto ansi sealed Func`1<+ TResult> extends System.MulticastDelegate" FrameworkAlternate="dotnet-uwp-10.0;net-5.0;net-6.0;net-7.0;net-8.0;net-9.0;netcore-1.0;netcore-1.1;netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0;netcore-3.1;netframework-4.0;netframework-4.5;netframework-4.5.1;netframework-4.5.2;netframework-4.6;netframework-4.6.1;netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1;netstandard-1.0;netstandard-1.1;netstandard-1.2;netstandard-1.3;netstandard-1.4;netstandard-1.5;netstandard-1.6;netstandard-2.0;netstandard-2.1" />
<TypeSignature Language="DocId" Value="T:System.Func`1" />
<TypeSignature Language="VB.NET" Value="Public Delegate Function Func(Of Out TResult)() As TResult " FrameworkAlternate="dotnet-uwp-10.0;net-5.0;net-6.0;net-7.0;net-8.0;net-9.0;netcore-1.0;netcore-1.1;netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0;netcore-3.1;netframework-4.0;netframework-4.5;netframework-4.5.1;netframework-4.5.2;netframework-4.6;netframework-4.6.1;netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1;netstandard-1.0;netstandard-1.1;netstandard-1.2;netstandard-1.3;netstandard-1.4;netstandard-1.5;netstandard-1.6;netstandard-2.0;netstandard-2.1" />
<TypeSignature Language="F#" Value="type Func<'Result> = delegate of unit -> 'Result" />
<TypeSignature Language="C++ CLI" Value="generic <typename TResult>
public delegate TResult Func();" />
<TypeSignature Language="C#" Value="public delegate TResult Func<TResult>();" FrameworkAlternate="netframework-3.5" />
<TypeSignature Language="ILAsm" Value=".class public auto ansi sealed Func`1<TResult> extends System.MulticastDelegate" FrameworkAlternate="netframework-3.5" />
<TypeSignature Language="VB.NET" Value="Public Delegate Function Func(Of TResult)() As TResult " FrameworkAlternate="netframework-3.5" />
<AssemblyInfo>
<AssemblyName>System.Runtime</AssemblyName>
<AssemblyVersion>4.0.0.0</AssemblyVersion>
<AssemblyVersion>4.0.10.0</AssemblyVersion>
<AssemblyVersion>4.0.20.0</AssemblyVersion>
<AssemblyVersion>4.1.0.0</AssemblyVersion>
<AssemblyVersion>4.2.0.0</AssemblyVersion>
<AssemblyVersion>4.2.1.0</AssemblyVersion>
<AssemblyVersion>4.2.2.0</AssemblyVersion>
<AssemblyVersion>5.0.0.0</AssemblyVersion>
<AssemblyVersion>6.0.0.0</AssemblyVersion>
<AssemblyVersion>7.0.0.0</AssemblyVersion>
<AssemblyVersion>8.0.0.0</AssemblyVersion>
<AssemblyVersion>9.0.0.0</AssemblyVersion>
</AssemblyInfo>
<AssemblyInfo>
<AssemblyName>mscorlib</AssemblyName>
<AssemblyVersion>2.0.5.0</AssemblyVersion>
<AssemblyVersion>4.0.0.0</AssemblyVersion>
</AssemblyInfo>
<AssemblyInfo>
<AssemblyName>netstandard</AssemblyName>
<AssemblyVersion>2.0.0.0</AssemblyVersion>
<AssemblyVersion>2.1.0.0</AssemblyVersion>
</AssemblyInfo>
<AssemblyInfo>
<AssemblyName>System.Core</AssemblyName>
<AssemblyVersion>3.5.0.0</AssemblyVersion>
</AssemblyInfo>
<TypeForwardingChain>
<TypeForwarding From="mscorlib" FromVersion="4.0.0.0" To="System.Runtime" ToVersion="0.0.0.0" FrameworkAlternate="dotnet-uwp-10.0" />
<TypeForwarding From="System.Core" FromVersion="4.0.0.0" To="System.Runtime" ToVersion="0.0.0.0" FrameworkAlternate="dotnet-uwp-10.0" />
<TypeForwarding From="netstandard" FromVersion="2.1.0.0" To="System.Runtime" ToVersion="5.0.0.0" FrameworkAlternate="net-5.0" />
<TypeForwarding From="netstandard" FromVersion="2.1.0.0" To="System.Runtime" ToVersion="6.0.0.0" FrameworkAlternate="net-6.0" />
<TypeForwarding From="netstandard" FromVersion="2.1.0.0" To="System.Runtime" ToVersion="7.0.0.0" FrameworkAlternate="net-7.0" />
<TypeForwarding From="netstandard" FromVersion="2.1.0.0" To="System.Runtime" ToVersion="8.0.0.0" FrameworkAlternate="net-8.0" />
<TypeForwarding From="netstandard" FromVersion="2.1.0.0" To="System.Runtime" ToVersion="9.0.0.0" FrameworkAlternate="net-9.0" />
<TypeForwarding From="System.Core" FromVersion="4.0.0.0" To="mscorlib" ToVersion="4.0.0.0" FrameworkAlternate="netframework-4.0;netframework-4.5;netframework-4.5.1;netframework-4.5.2;netframework-4.6;netframework-4.6.1;netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1" />
<TypeForwarding From="System.Runtime" FromVersion="4.1.1.1" To="mscorlib" ToVersion="4.0.0.0" FrameworkAlternate="netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1" />
</TypeForwardingChain>
<TypeParameters>
<TypeParameter Name="TResult">
<Constraints>
<ParameterAttribute>Covariant</ParameterAttribute>
</Constraints>
<Attributes>
<Attribute FrameworkAlternate="net-8.0;net-9.0">
<AttributeName Language="C#">[System.Runtime.CompilerServices.Nullable(2)]</AttributeName>
<AttributeName Language="F#">[<System.Runtime.CompilerServices.Nullable(2)>]</AttributeName>
</Attribute>
</Attributes>
</TypeParameter>
</TypeParameters>
<Base>
<BaseTypeName>System.Delegate</BaseTypeName>
</Base>
<Attributes>
<Attribute FrameworkAlternate="netframework-4.0;netframework-4.5;netframework-4.5.1;netframework-4.5.2;netframework-4.6;netframework-4.6.1;netframework-4.6.2;netframework-4.7;netframework-4.7.1;netframework-4.7.2;netframework-4.8;netframework-4.8.1">
<AttributeName Language="C#">[System.Runtime.CompilerServices.TypeForwardedFrom("System.Core, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=b77a5c561934e089")]</AttributeName>
<AttributeName Language="F#">[<System.Runtime.CompilerServices.TypeForwardedFrom("System.Core, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=b77a5c561934e089")>]</AttributeName>
</Attribute>
</Attributes>
<Parameters />
<ReturnValue>
<ReturnType>TResult</ReturnType>
</ReturnValue>
<Docs>
<typeparam name="TResult">The type of the return value of the method that this delegate encapsulates.</typeparam>
<summary>Encapsulates a method that has no parameters and returns a value of the type specified by the <typeparamref name="TResult" /> parameter.</summary>
<returns>The return value of the method that this delegate encapsulates.</returns>
<remarks>
<format type="text/markdown"><![CDATA[
## Remarks
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 no parameters and must return a value.
> [!NOTE]
> To reference a method that has no parameters and returns `void` (`unit`, in F#) (or in Visual Basic, that is declared as a `Sub` rather than as a `Function`), use the <xref:System.Action> delegate instead.
When you use the <xref:System.Func%601> delegate, you do not have to explicitly define a delegate that encapsulates a parameterless method. For example, the following code explicitly declares a delegate named `WriteMethod` and assigns a reference to the `OutputTarget.SendToFile` instance method to its delegate instance.
:::code language="csharp" source="~/snippets/csharp/System/FuncTResult/Overview/Delegate.cs" interactive="try-dotnet" id="Snippet1":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~1/fs/Delegate.fs" id="Snippet1":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~1/vb/Delegate.vb" id="Snippet1":::
The following example simplifies this code by instantiating the <xref:System.Func%601> delegate instead of explicitly defining a new delegate and assigning a named method to it.
:::code language="csharp" source="~/snippets/csharp/System/FuncTResult/Overview/Func1.cs" interactive="try-dotnet" id="Snippet2":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~1/fs/Func1.fs" id="Snippet2":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~1/vb/Func1.vb" id="Snippet2":::
You can use the <xref:System.Func%601> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see [Anonymous Methods](/dotnet/csharp/programming-guide/statements-expressions-operators/anonymous-methods).)
:::code language="csharp" source="~/snippets/csharp/System/FuncTResult/Overview/Anon.cs" interactive="try-dotnet" id="Snippet3":::
You can also assign a lambda expression to a <xref:System.Func%602> delegate, as the following example illustrates. (For an introduction to lambda expressions, see [Lambda Expressions (VB)](/dotnet/visual-basic/programming-guide/language-features/procedures/lambda-expressions), [Lambda Expressions (C#)](/dotnet/csharp/programming-guide/statements-expressions-operators/lambda-expressions), and [Lambda Expressions (F#)](/dotnet/fsharp/language-reference/functions/lambda-expressions-the-fun-keyword/).)
:::code language="csharp" source="~/snippets/csharp/System/FuncTResult/Overview/Lambda.cs" interactive="try-dotnet" id="Snippet4":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~1/fs/Lambda.fs" id="Snippet4":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~1/vb/Lambda.vb" id="Snippet4":::
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 <xref:System.Linq> namespace have `Func` parameters, you can pass these methods a lambda expression without explicitly instantiating a `Func` delegate.
If you have an expensive computation that you want to execute only if the result is actually needed, you can assign the expensive function to a <xref:System.Func%601> delegate. The execution of the function can then be delayed until a property that accesses the value is used in an expression. The example in the next section demonstrates how to do this.
## Examples
The following example demonstrates how to use a delegate that takes no parameters. This code creates a generic class named `LazyValue` that has a field of type <xref:System.Func%601>. This delegate field can store a reference to any function that returns a value of the type that corresponds to the type parameter of the `LazyValue` object. The `LazyValue` type also has a `Value` property that executes the function (if it has not already been executed) and returns the resulting value.
The example creates two methods and instantiates two `LazyValue` objects with lambda expressions that call these methods. The lambda expressions do not take parameters because they just need to call a method. As the output shows, the two methods are executed only when the value of each `LazyValue` object is retrieved.
:::code language="csharp" source="~/snippets/csharp/System/FuncTResult/Overview/Example.cs" interactive="try-dotnet" id="Snippet5":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~1/fs/Example.fs" id="Snippet5":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~1/vb/Example.vb" id="Snippet5":::
]]></format>
</remarks>
<related type="Article" href="/dotnet/csharp/programming-guide/statements-expressions-operators/lambda-expressions">Lambda Expressions (C# Programming Guide)</related>
<related type="Article" href="/dotnet/fsharp/language-reference/functions/lambda-expressions-the-fun-keyword">Lambda Expressions: The fun Keyword (F#)</related>
<related type="Article" href="/dotnet/visual-basic/programming-guide/language-features/procedures/lambda-expressions">Lambda Expressions</related>
<related type="Article" href="/dotnet/csharp/programming-guide/delegates/">Delegates (C# Programming Guide)</related>
<related type="Article" href="/dotnet/fsharp/language-reference/delegates/">Delegates (F#)</related>
<related type="Article" href="/dotnet/visual-basic/programming-guide/language-features/delegates/">Delegates in Visual Basic</related>
</Docs>
</Type>