dotnet · BillWagner · Mar 7, 2022 · Mar 5, 2022
@@ -0,0 +1,124 @@
+// <Snippet1>
+module Test
+
+open System
+
+// Define a delegate to handle string display.
+type CheckAndDisplayDelegate = delegate of string -> unit
+
+type StringContainer() =
+    // A generic ResizeArray object that holds the strings.
+    let container = ResizeArray()
+
+    // A method that adds strings to the collection.
+    member _.AddString(str) =
+        container.Add str
+
+    // Iterate through the strings and invoke the method(s) that the delegate points to.
+    member _.DisplayAllQualified(displayDelegate: CheckAndDisplayDelegate) =
+        for str in container do
+            displayDelegate.Invoke str
+
+// This module defines some functions to display strings.
+module StringExtensions =
+    // Display a string if it starts with a consonant.
+    let conStart (str: string) =
+        match str[0] with
+        | 'a' | 'e' | 'i' | 'o' | 'u' -> ()
+        | _ -> printfn $"{str}"
+
+    // Display a string if it starts with a vowel.
+    let vowelStart (str: string) =
+        match str[0] with
+        | 'a' | 'e' | 'i' | 'o' | 'u' -> printfn $"{str}"
+        | _ -> ()
+
+// Demonstrate the use of delegates, including the Remove and
+// Combine methods to create and modify delegate combinations.
+[<EntryPoint>]
+let main _ =
+    // Declare the StringContainer class and add some strings
+    let container = StringContainer()
+    container.AddString "This"
+    container.AddString "is"
+    container.AddString "a"
+    container.AddString "multicast"
+    container.AddString "delegate"
+    container.AddString "example"
+
+    // Create two delegates individually using different methods.
+    let conStart = CheckAndDisplayDelegate StringExtensions.conStart
+    let vowelStart = CheckAndDisplayDelegate StringExtensions.vowelStart 
+
+    // Get the list of all delegates assigned to this MulticastDelegate instance.
+    let delegateList = conStart.GetInvocationList()
+    printfn $"conStart contains {delegateList.Length} delegate(s)."
+    let delegateList = vowelStart.GetInvocationList()
+    printfn $"vowelStart contains {delegateList.Length} delegate(s).\n"
+
+    // Determine whether the delegates are System.Multicast delegates.
+    if box conStart :? System.MulticastDelegate && box vowelStart :? System.MulticastDelegate then
+        printfn "conStart and vowelStart are derived from MulticastDelegate.\n"
+
+    // Execute the two delegates.
+    printfn "Executing the conStart delegate:"
+    container.DisplayAllQualified conStart
+    printfn "\nExecuting the vowelStart delegate:"
+    container.DisplayAllQualified vowelStart
+    printfn ""
+
+    // Create a new MulticastDelegate and call Combine to add two delegates.
+    let multipleDelegates =
+        Delegate.Combine(conStart, vowelStart) :?> CheckAndDisplayDelegate
+
+    // How many delegates does multipleDelegates contain?
+    let delegateList = multipleDelegates.GetInvocationList()
+    printfn $"\nmultipleDelegates contains {delegateList.Length} delegates.\n"
+
+    // Pass this multicast delegate to DisplayAllQualified.
+    printfn "Executing the multipleDelegate delegate."
+    container.DisplayAllQualified multipleDelegates
+
+    // Call remove and combine to change the contained delegates.
+    let multipleDelegates = Delegate.Remove(multipleDelegates, vowelStart) :?> CheckAndDisplayDelegate
+    let multipleDelegates = Delegate.Combine(multipleDelegates, conStart) :?> CheckAndDisplayDelegate
+
+    // Pass multipleDelegates to DisplayAllQualified again.
+    printfn "\nExecuting the multipleDelegate delegate with two conStart delegates:"
+    printfn $"{multipleDelegates}"
+    0
+// The example displays the following output:
+//    conStart contains 1 delegate(s).
+//    vowelStart contains 1 delegate(s).
+//
+//    conStart and vowelStart are derived from MulticastDelegate.
+//
+//    Executing the conStart delegate:
+//    This
+//    multicast
+//    delegate
+//
+//    Executing the vowelStart delegate:
+//    is
+//    a
+//    example
+//
+//
+//    multipleDelegates contains 2 delegates.
+//
+//    Executing the multipleDelegate delegate.
+//    This
+//    is
+//    a
+//    multicast
+//    delegate
+//    example
+//
+//    Executing the multipleDelegate delegate with two conStart delegates:
+//    This
+//    This
+//    multicast
+//    multicast
+//    delegate
+//    delegate
+// </Snippet1>
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="delegatestring.fs" />
+  </ItemGroup>
+</Project>
@@ -79,6 +79,7 @@
 
  :::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR/Multicast Delegate Introduction/CPP/delegatestring.cpp" id="Snippet1":::
  :::code language="csharp" source="~/snippets/csharp/System/MulticastDelegate/Overview/delegatestring.cs" interactive="try-dotnet" id="Snippet1":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/MulticastDelegate/Overview/delegatestring.fs" id="Snippet1":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR/Multicast Delegate Introduction/VB/delegatestring.vb" id="Snippet1":::
 
  ]]></format>