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Func`2.xml
148 lines (132 loc) · 13.2 KB
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Func`2.xml
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<Type Name="Func<T,TResult>" FullName="System.Func<T,TResult>">
<TypeSignature Language="C#" Value="public delegate TResult Func<in T,out TResult>(T arg);" 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`2<- T, + 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`2" />
<TypeSignature Language="VB.NET" Value="Public Delegate Function Func(Of In T, Out TResult)(arg As T) 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<'T, 'Result> = delegate of 'T -> 'Result" />
<TypeSignature Language="C++ CLI" Value="generic <typename T, typename TResult>
public delegate TResult Func(T arg);" />
<TypeSignature Language="C#" Value="public delegate TResult Func<T,TResult>(T arg);" FrameworkAlternate="netframework-3.5" />
<TypeSignature Language="ILAsm" Value=".class public auto ansi sealed Func`2<T, TResult> extends System.MulticastDelegate" FrameworkAlternate="netframework-3.5" />
<TypeSignature Language="VB.NET" Value="Public Delegate Function Func(Of T, TResult)(arg As T) 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="T">
<Constraints>
<ParameterAttribute>Contravariant</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>
<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>
<Parameter Name="arg" Type="T" />
</Parameters>
<ReturnValue>
<ReturnType>TResult</ReturnType>
</ReturnValue>
<Docs>
<typeparam name="T">The type of the parameter of the method that this delegate encapsulates.</typeparam>
<typeparam name="TResult">The type of the return value of the method that this delegate encapsulates.</typeparam>
<param name="arg">The parameter of the method that this delegate encapsulates.</param>
<summary>Encapsulates a method that has one parameter 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 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 <xref:System.Action%601> delegate instead.
When you use the <xref:System.Func%602> 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.
:::code language="csharp" source="~/snippets/csharp/System/FuncT,TResult/Overview/Delegate.cs" interactive="try-dotnet" id="Snippet1":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~2/fs/Delegate.fs" id="Snippet1":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~2/vb/Delegate.vb" id="Snippet1":::
The following example simplifies this code by instantiating the <xref:System.Func%602> delegate instead of explicitly defining a new delegate and assigning a named method to it.
:::code language="csharp" source="~/snippets/csharp/System/FuncT,TResult/Overview/Func2_1.cs" interactive="try-dotnet-method" id="Snippet2":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~2/fs/Func2_1.fs" id="Snippet2":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~2/vb/Func2_1.vb" id="Snippet2":::
You can also use the <xref:System.Func%602> 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/FuncT,TResult/Overview/Anon.cs" interactive="try-dotnet-method" 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/FuncT,TResult/Overview/Lambda.cs" interactive="try-dotnet-method" id="Snippet4":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~2/fs/Lambda.fs" id="Snippet4":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~2/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 <xref:System.Func%602> parameters, you can pass these methods a lambda expression without explicitly instantiating a <xref:System.Func%602> delegate.
## Examples
The following example demonstrates how to declare and use a <xref:System.Func%602> delegate. This example declares a <xref:System.Func%602> 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 <xref:System.Linq.Enumerable.Select%2A?displayProperty=nameWithType> method to change the strings in an array of strings to uppercase.
:::code language="csharp" source="~/snippets/csharp/System/FuncT,TResult/Overview/Example.cs" interactive="try-dotnet-method" id="Snippet5":::
:::code language="fsharp" source="~/snippets/fsharp/VS_Snippets_CLR_System/system.Func~2/fs/Example.fs" id="Snippet5":::
:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.Func~2/vb/Example.vb" id="Snippet5":::
:::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.Func~2/cpp/Example.cpp" id="Snippet6":::
]]></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 (Visual Basic)</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 (Visual Basic)</related>
</Docs>
</Type>