WeakReference F# snippets (dotnet#8077)

Author: albert-du

snippets/fsharp/System/WeakReference/Overview/fs.fsproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="program.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System/WeakReference/Overview/program.fs

@@ -0,0 +1,86 @@
+// <Snippet1>
+open System
+open System.Collections.Generic
+
+// This class creates byte arrays to simulate data.
+type Data(size) =
+    let _data = Array.zeroCreate<byte> (size * 1024)
+    
+    // Simple property.
+    member _.Name = 
+        string size
+
+type Cache(count) =
+    // Dictionary to contain the cache.
+    static let mutable _cache = Dictionary<int, WeakReference>()
+
+    // Track the number of times an object is regenerated.
+    let mutable regenCount = 0
+
+    do
+        _cache <- Dictionary<int, WeakReference>()
+        // <Snippet2>
+        // Add objects with a short weak reference to the cache.
+        for i = 0 to count - 1 do
+            _cache.Add(i, WeakReference(Data i, false))
+        // </Snippet2>
+
+    // Number of items in the cache.
+    member _.Count =
+        _cache.Count
+
+    // Number of times an object needs to be regenerated.
+    member _.RegenerationCount =
+        regenCount
+
+    // Retrieve a data object from the cache.
+    member _.Item
+        with get (index) =
+            // <Snippet3>
+            match _cache[index].Target with
+            | :? Data as d->
+                // Object was obtained with the weak reference.
+                printfn $"Regenerate object at {index}: No"
+                d
+            | _ ->
+                // If the object was reclaimed, generate a new one.
+                printfn $"Regenerate object at {index}: Yes"
+                let d = Data index
+                _cache[index].Target <- d
+                regenCount <- regenCount + 1
+                d 
+            // </Snippet3>
+
+// Create the cache.
+let cacheSize = 50
+let r = Random()
+let c = Cache cacheSize
+
+let mutable dataName = ""
+GC.Collect 0
+
+// Randomly access objects in the cache.
+for _ = 0 to c.Count - 1 do
+    let index = r.Next c.Count
+
+    // Access the object by getting a property value.
+    dataName <- c[index].Name
+
+// Show results.
+let regenPercent = double c.RegenerationCount / double c.Count
+printfn $"Cache size: {c.Count}, Regenerated: {regenPercent:P2}%%"
+
+// Example of the last lines of the output:
+//
+// ...
+// Regenerate object at 36: Yes
+// Regenerate object at 8: Yes
+// Regenerate object at 21: Yes
+// Regenerate object at 4: Yes
+// Regenerate object at 38: No
+// Regenerate object at 7: Yes
+// Regenerate object at 2: Yes
+// Regenerate object at 43: Yes
+// Regenerate object at 38: No
+// Cache size: 50, Regenerated: 94%
+// </Snippet1>

xml/System/WeakReference.xml

@@ -76,6 +76,7 @@
  The example randomly accesses objects in the cache. If an object is reclaimed for garbage collection, a new data object is regenerated; otherwise, the object is available to access because of the weak reference.  
   
  :::code language="csharp" source="~/snippets/csharp/System/WeakReference/Overview/program.cs" id="Snippet1":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/WeakReference/Overview/program.fs" id="Snippet1":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR/WeakReference/vb/Module1.vb" id="Snippet1":::  
   
  ]]></format>
@@ -227,6 +228,7 @@
  The following example creates a cache of data objects with short weak references. This example is part of a larger example provided for the <xref:System.WeakReference> class.  
   
  :::code language="csharp" source="~/snippets/csharp/System/WeakReference/Overview/program.cs" id="Snippet2":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/WeakReference/Overview/program.fs" id="Snippet2":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR/WeakReference/vb/Module1.vb" id="Snippet2":::  
   
  ]]></format>
@@ -529,6 +531,7 @@
  The following example tries to obtain an object from a cache of objects with weak references. If the object was reclaimed for garbage collection, a new object is generated. This example is part of a larger example provided for the <xref:System.WeakReference> class.  
   
  :::code language="csharp" source="~/snippets/csharp/System/WeakReference/Overview/program.cs" id="Snippet3":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/WeakReference/Overview/program.fs" id="Snippet3":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR/WeakReference/vb/Module1.vb" id="Snippet3":::  
   
  ]]></format>