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Nov 12, 2021
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Add System.Action<T> F# snippets #7380

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0d12303
Add System.Action<T> F# snippets
albert-du Nov 4, 2021
d796096
Update Lambda.fs
albert-du Nov 11, 2021
c0bcb80
Update action.fs
albert-du Nov 11, 2021
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30 changes: 30 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action_PrintExample/fs/action.fs
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open System

//<snippet01>
// F# provides a type alias for System.Collections.List<'T> as ResizeArray<'T>.
let names = ResizeArray<string>()
names.Add "Bruce"
names.Add "Alfred"
names.Add "Tim"
names.Add "Richard"

let print s = printfn "%s" s

// Display the contents of the list using the print function.
names.ForEach(Action<string> print)

// The following demonstrates the lambda expression feature of F#
// to display the contents of the list to the console.
names.ForEach(fun s -> printfn "%s" s)

(* This code will produce output similar to the following:
* Bruce
* Alfred
* Tim
* Richard
* Bruce
* Alfred
* Tim
* Richard
*)
//</snippet01>
12 changes: 12 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action_PrintExample/fs/action.fsproj
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<Project Sdk="Microsoft.NET.Sdk">

<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
</PropertyGroup>

<ItemGroup>
<Compile Include="action.fs" />
</ItemGroup>

</Project>
20 changes: 20 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Action1.fs
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module TestAction1

// <Snippet2>
open System
open System.Windows.Forms

let showWindowsMessage message =
MessageBox.Show message |> ignore

let messageTarget =
Action<string>(
if Environment.GetCommandLineArgs().Length > 1 then
showWindowsMessage
else
printfn "%s"
)

messageTarget.Invoke "Hello, World!"

// </Snippet2>
16 changes: 16 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Action1.fsproj
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<Project Sdk="Microsoft.NET.Sdk">

<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0-windows</TargetFramework>
<DisableWinExeOutputInference>true</DisableWinExeOutputInference>
<UseWindowsForms>true</UseWindowsForms>
</PropertyGroup>

<ItemGroup>
<Compile Include="Action1.fs" />
<Compile Include="Delegate.fs" />
<Compile Include="Lambda.fs" />
</ItemGroup>

</Project>
22 changes: 22 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Delegate.fs
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module TestCustomDelegate

// <Snippet1>
open System
open System.Windows.Forms

type DisplayMessage = delegate of message: string -> unit

let showWindowsMessage message =
MessageBox.Show message |> ignore

let messageTarget =
DisplayMessage(
if Environment.GetCommandLineArgs().Length > 1 then
showWindowsMessage
else
printfn "%s"
)

messageTarget.Invoke "Hello, World!"

// </Snippet1>
20 changes: 20 additions & 0 deletions samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Lambda.fs
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module TestLambdaExpression

// <Snippet4>
open System
open System.Windows.Forms

let showWindowsMessage message =
MessageBox.Show message |> ignore

let messageTarget =
Action<string>(
if Environment.GetCommandLineArgs().Length > 1 then
fun s -> showWindowsMessage s
else
fun s -> printfn "%s" s
)

messageTarget.Invoke "Hello, World!"

// </Snippet4>
4 changes: 4 additions & 0 deletions xml/System/Action`1.xml
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Expand Up @@ -69,12 +69,14 @@

:::code language="cpp" source="~/samples/snippets/cpp/VS_Snippets_CLR_System/system.Action~1/cpp/delegate.cpp" id="Snippet1":::
:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.Action~1/cs/Delegate.cs" id="Snippet1":::
:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Delegate.fs" id="Snippet1":::
:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Action~1/vb/Delegate.vb" id="Snippet1":::

The following example simplifies this code by instantiating the <xref:System.Action%601> delegate instead of explicitly defining a new delegate and assigning a named method to it.

:::code language="cpp" source="~/samples/snippets/cpp/VS_Snippets_CLR_System/system.Action~1/cpp/action`1.cpp" id="Snippet2":::
:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.Action~1/cs/Action1.cs" id="Snippet2":::
:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Action1.fs" id="Snippet2":::
:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Action~1/vb/Action1.vb" id="Snippet2":::

You can also use the <xref:System.Action%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).)
Expand All @@ -84,6 +86,7 @@
You can also assign a lambda expression to an <xref:System.Action%601> delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see [Lambda Expressions](/dotnet/csharp/programming-guide/statements-expressions-operators/lambda-expressions).)

:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.Action~1/cs/Lambda.cs" id="Snippet4":::
:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action~1/fs/Lambda.fs" id="Snippet4":::
:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Action~1/vb/lambda.vb" id="Snippet4":::

The <xref:System.Collections.Generic.List%601.ForEach%2A> and <xref:System.Array.ForEach%2A> methods each take an <xref:System.Action%601> delegate as a parameter. The method encapsulated by the delegate allows you to perform an action on each element in the array or list. The example uses the <xref:System.Collections.Generic.List%601.ForEach%2A> method to provide an illustration.
Expand All @@ -94,6 +97,7 @@
The following example demonstrates the use of the <xref:System.Action%601> delegate to print the contents of a <xref:System.Collections.Generic.List%601> object. In this example, the `Print` method is used to display the contents of the list to the console. In addition, the C# example also demonstrates the use of anonymous methods to display the contents to the console. Note that the example does not explicitly declare an <xref:System.Action%601> variable. Instead, it passes a reference to a method that takes a single parameter and that does not return a value to the <xref:System.Collections.Generic.List%601.ForEach%2A?displayProperty=nameWithType> method, whose single parameter is an <xref:System.Action%601> delegate. Similarly, in the C# example, an <xref:System.Action%601> delegate is not explicitly instantiated because the signature of the anonymous method matches the signature of the <xref:System.Action%601> delegate that is expected by the <xref:System.Collections.Generic.List%601.ForEach%2A?displayProperty=nameWithType> method.

:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.Action_PrintExample/cs/action.cs" interactive="try-dotnet-method" id="Snippet01":::
:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.Action_PrintExample/fs/action.fs" id="Snippet01":::
:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Action_PrintExample/vb/action.vb" id="Snippet01":::

]]></format>
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