SortingGenericList: .NET 10, comparer null contract fix, IndexOf duplicates

collections-lists/SortingGenericList/src/SortingGenericList.Console/Program.cs

@@ -43,6 +43,22 @@
 PrintProducts(productList);
 Console.WriteLine();
 
+Console.WriteLine("----------List<Product> In Place Sort With Comparer<T>.Create (Order: Price - Descending)----------");
+Console.WriteLine("Products:");
+PrintProducts(unsortedProducts);
+Console.WriteLine();
+
+productList.Clear();
+productList.AddRange(unsortedProducts);
+
+var byPriceDescending = Comparer<Product?>.Create(
+    (a, b) => Nullable.Compare(b?.Price, a?.Price));
+
+productList.Sort(byPriceDescending);
+Console.WriteLine("**Sorted**");
+PrintProducts(productList);
+Console.WriteLine();
+
 Console.WriteLine("----------List<Product> In Place Sort With Comparison<T> (Lambda: Order - Category)----------");
 Console.WriteLine("Products:");
 PrintProducts(unsortedProducts);

collections-lists/SortingGenericList/src/SortingGenericList.Console/SortingGenericList.Console.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <OutputType>Exe</OutputType>
-        <TargetFramework>net7.0</TargetFramework>
+        <TargetFramework>net10.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
     </PropertyGroup>

collections-lists/SortingGenericList/src/SortingGenericList.Library/DataModels/Product.cs

@@ -14,7 +14,7 @@ public sealed record Product(string ProductName, string Category, decimal Price)
     public static bool operator >=(Product? left, Product? right) =>
         Comparer<Product>.Default.Compare(left, right) >= 0;
 
-    public static int DescendingCompare(Product? a, Product? b) => b?.CompareTo(a) ?? -1;
+    public static int DescendingCompare(Product? a, Product? b) => Comparer<Product>.Default.Compare(b, a);
 
     public int CompareTo(object? obj)
     {

collections-lists/SortingGenericList/src/SortingGenericList.Library/MySortedList.cs

@@ -48,8 +48,12 @@ public void CopyTo(Span<T> dest)
     public int IndexOf(T item)
     {
         var index = _list.BinarySearch(item, _comparer);
+        if (index < 0) return -1;
 
-        return index < 0 ? -1 : index;
+        var comparer = _comparer ?? Comparer<T>.Default;
+        while (index > 0 && comparer.Compare(_list[index - 1], item) == 0) index--;
+
+        return index;
     }
 
     public void Insert(int index, T item)

collections-lists/SortingGenericList/src/SortingGenericList.Library/SortingGenericList.Library.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net7.0</TargetFramework>
+        <TargetFramework>net10.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
     </PropertyGroup>

collections-lists/SortingGenericList/test/SortingGenericList.Test/DataModelsTests/ProductTests.cs

@@ -6,7 +6,7 @@ public sealed class ProductTests
     public void Product_Default_Id_Should_Not_Be_Empty()
     {
         var product = new Product("Product A", "Category1", 10.0m);
-        product.Id.Should().NotBeEmpty();
+        Assert.NotEqual(Guid.Empty, product.Id);
     }
 
     [Fact]
@@ -16,26 +16,26 @@ public void Product_Comparisons_Should_Be_Correct()
         var product2 = new Product("Product B", "Category1", 10.0m);
         var product3 = new Product("Product A", "Category1", 20.0m);
 
-        product1.Should().BeLessThan(product2);
-        product1.Should().BeLessOrEqualTo(product2);
-        product2.Should().BeGreaterThan(product1);
-        product2.Should().BeGreaterOrEqualTo(product1);
+        Assert.True(product1 < product2);
+        Assert.True(product1 <= product2);
+        Assert.True(product2 > product1);
+        Assert.True(product2 >= product1);
 
-        product1.Should().NotBe(product3);
-        product1.CompareTo(product3).Should().BeNegative();
+        Assert.NotEqual(product1, product3);
+        Assert.True(product1.CompareTo(product3) < 0);
 
-        product1.CompareTo(product1).Should().Be(0);
+        Assert.Equal(0, product1.CompareTo(product1));
     }
 
     [Fact]
     public void Product_Comparison_With_Null_Should_Be_Correct()
     {
         var product = new Product("Product A", "Category1", 10.0m);
 
-        product.Invoking(p => p.CompareTo(new object()))
-               .Should().Throw<ArgumentException>().WithMessage($"Object must be of type {nameof(Product)}");
+        var exception = Assert.Throws<ArgumentException>(() => product.CompareTo(new object()));
+        Assert.Equal($"Object must be of type {nameof(Product)}", exception.Message);
 
-        product.CompareTo(null).Should().Be(1);
+        Assert.Equal(1, product.CompareTo(null));
     }
 
     [Fact]
@@ -46,7 +46,7 @@ public void ShouldCorrectlyPerformDescendComparison_ForSameProducts_Ascending()
 
         var result = Product.DescendingCompare(product1, product2);
 
-        result.Should().BePositive();
+        Assert.True(result > 0);
     }
 
     [Fact]
@@ -57,7 +57,7 @@ public void ShouldCorrectlyPerformDescendComparison_ForSameProducts_Descending()
 
         var result = Product.DescendingCompare(product1, product2);
 
-        result.Should().BeNegative();
+        Assert.True(result < 0);
     }
 
     [Fact]
@@ -68,6 +68,30 @@ public void ShouldCorrectlyPerformDescendComparison_ForEqualProducts()
 
         var result = Product.DescendingCompare(product1, product2);
 
-        result.Should().Be(0);
+        Assert.Equal(0, result);
     }
-}
+
+    [Fact]
+    public void DescendingCompare_ForTwoNulls_ReturnsZero()
+    {
+        Assert.Equal(0, Product.DescendingCompare(null, null));
+    }
+
+    [Fact]
+    public void DescendingCompare_WhenListHasManyNulls_SortsWithNullsLast()
+    {
+        var random = new Random(1);
+        var products = Enumerable.Range(0, 200)
+            .Select(i => i % 5 == 0 ? null : new Product($"P{random.Next(1000):D3}", "Category", 1m))
+            .ToList();
+
+        products.Sort(Product.DescendingCompare);
+
+        Assert.All(products.Take(160), Assert.NotNull);
+        Assert.All(products.Skip(160), Assert.Null);
+        Assert.Equal(
+            products.Take(160).OrderByDescending(p => p!.ProductName, StringComparer.OrdinalIgnoreCase)
+                .Select(p => p!.ProductName),
+            products.Take(160).Select(p => p!.ProductName));
+    }
+}