Allow use of C# 13

Author: atifaziz

Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <LangVersion>12</LangVersion>
+    <LangVersion>13</LangVersion>
     <Nullable>enable</Nullable>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <AnalysisLevel>8.0-all</AnalysisLevel>

MoreLinq/Experimental/Memoize.cs

@@ -65,7 +65,7 @@ public static IEnumerable<T> Memoize<T>(this IEnumerable<T> source) =>
     sealed class MemoizedEnumerable<T>(IEnumerable<T> sequence) : IEnumerable<T>, IDisposable
     {
         List<T>? cache;
-        readonly object locker = new();
+        readonly Lock locker = new();
         readonly IEnumerable<T> source = sequence ?? throw new ArgumentNullException(nameof(sequence));
         IEnumerator<T>? sourceEnumerator;
         int? errorIndex;
@@ -77,7 +77,9 @@ public IEnumerator<T> GetEnumerator()
             {
                 lock (this.locker)
                 {
+#pragma warning disable CA1508 // Avoid dead conditional code
                     if (this.cache == null)
+#pragma warning restore CA1508 // Avoid dead conditional code
                     {
                         this.error?.Throw();
 

MoreLinq/Lock.cs

@@ -0,0 +1,8 @@
+#if NET9_0_OR_GREATER
+// https://learn.microsoft.com/dotnet/csharp/language-reference/statements/lock#guidelines
+global using Lock = System.Threading.Lock;
+#else
+// For why "System.Object" instead of "object", see:
+// https://github.com/dotnet/runtime/issues/110242
+global using Lock = System.Object;
+#endif