Add Delegate.HasSingleTarget (#270)

apiCount.include.md

@@ -1 +1 @@
-**API count: 433**
+**API count: 434**

api_list.include.md

@@ -68,6 +68,11 @@
  * `bool TryFormat(decimal, Span<char>, int, ReadOnlySpan<char>, IFormatProvider?)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.decimal.tryformat#system-decimal-tryformat(system-span((system-char))-system-int32@-system-readonlyspan((system-char))-system-iformatprovider))
 
 
+#### Delegate
+
+ * `bool HasSingleTarget(Delegate)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.delegate.hassingletarget)
+
+
 #### Dictionary<TKey, TValue>
 
  * `bool Remove<TKey, TValue>(Dictionary<TKey, TValue>, TKey, TValue) where TKey : notnull` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.remove)

readme.md

@@ -12,7 +12,7 @@ The package targets `netstandard2.0` and is designed to support the following ru
  * `net5.0`, `net6.0`, `net7.0`, `net8.0`, `net9.0`
 
 
-**API count: 433**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
+**API count: 434**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
 
 
 **See [Milestones](../../milestones?state=closed) for release notes.**
@@ -537,6 +537,11 @@ The class `Polyfill` includes the following extension methods:
  * `bool TryFormat(decimal, Span<char>, int, ReadOnlySpan<char>, IFormatProvider?)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.decimal.tryformat#system-decimal-tryformat(system-span((system-char))-system-int32@-system-readonlyspan((system-char))-system-iformatprovider))
 
 
+#### Delegate
+
+ * `bool HasSingleTarget(Delegate)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.delegate.hassingletarget)
+
+
 #### Dictionary<TKey, TValue>
 
  * `bool Remove<TKey, TValue>(Dictionary<TKey, TValue>, TKey, TValue) where TKey : notnull` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.remove)

src/Polyfill/Polyfill_Delegate.cs

@@ -0,0 +1,26 @@
+// <auto-generated />
+
+using System.Runtime.CompilerServices;
+
+#pragma warning disable
+
+namespace Polyfills;
+
+using System;
+using System.Collections.Concurrent;
+
+static partial class Polyfill
+{
+    /// <summary>
+    /// Gets a value that indicates whether the Delegate has a single invocation target.
+    /// </summary>
+    //Link: https://learn.microsoft.com/en-us/dotnet/api/system.delegate.hassingletarget
+    public static bool HasSingleTarget(this Delegate target)
+    {
+#if NET9_0_OR_GREATER
+        return target.HasSingleTarget;
+#else
+        return target.GetInvocationList().Length == 1;
+#endif
+    }
+}

src/Tests/PolyfillTests_Delegate.cs

@@ -0,0 +1,23 @@
+partial class PolyfillTests
+{
+    public static event EventHandler? MyEvent;
+
+    [Test]
+    public void HasSingleTarget()
+    {
+        MyEvent += Handler;
+        Assert.IsTrue(MyEvent.HasSingleTarget());
+        MyEvent += Handler;
+        Assert.IsFalse(MyEvent.HasSingleTarget());
+        var action = () =>
+        {
+        };
+        Assert.IsTrue(action.HasSingleTarget());
+        action += action;
+        Assert.IsFalse(action.HasSingleTarget());
+    }
+
+    static void Handler(object? sender, EventArgs e)
+    {
+    }
+}