Feat: IsNullableReferenceType

Author: AnnaSasDev

src/CodeOfChaos.Extensions/ReflectionHelpers.cs

@@ -0,0 +1,32 @@
+// ---------------------------------------------------------------------------------------------------------------------
+// Imports
+// ---------------------------------------------------------------------------------------------------------------------
+using System.Reflection;
+
+namespace CodeOfChaos.Extensions;
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Code
+// ---------------------------------------------------------------------------------------------------------------------
+public static class ReflectionHelper {
+    public static bool IsNullableReferenceType(this ParameterInfo parameter) {
+        // Value types can't be nullable reference types
+        if (parameter.ParameterType.IsValueType)
+            return false;
+
+        // Check if NullableAttribute exists on this parameter
+        CustomAttributeData? nullableAttribute = parameter.GetCustomAttributesData()
+            .FirstOrDefault(attr => attr.AttributeType.FullName == "System.Runtime.CompilerServices.NullableAttribute");
+
+        // If there is no NullableAttribute, treat it as non-nullable
+        if (nullableAttribute == null || nullableAttribute.ConstructorArguments.Count == 0)
+            return false;
+
+        // NullableAttribute encodes nullability flags; we need the first value for this parameter
+        byte? nullabilityFlag = nullableAttribute.ConstructorArguments[0].Value as byte? ;
+
+        // "2" = Nullable; "0" = Non-nullable; "1" = Oblivious (treat as non-nullable in this context)
+        return nullabilityFlag == 2;
+
+    }
+}

tests/Tests.CodeOfChaos.Extensions/ReflectionHelperTests.cs

@@ -0,0 +1,68 @@
+// ---------------------------------------------------------------------------------------------------------------------
+// Imports
+// ---------------------------------------------------------------------------------------------------------------------
+using CodeOfChaos.Extensions;
+using System.Reflection;
+
+namespace Tests.CodeOfChaos.Extensions;
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Code
+// ---------------------------------------------------------------------------------------------------------------------
+public class ReflectionHelperTests {
+    private class TestClass
+    {
+        // ReSharper disable UnusedParameter.Local
+        public static void MethodWithNullability(
+            string nonNullable, 
+            string? nullable, 
+            int valueType) 
+        { }
+    }
+
+    // -----------------------------------------------------------------------------------------------------------------
+    // Methods
+    // -----------------------------------------------------------------------------------------------------------------
+    [Test]
+    public async Task IsNullableReferenceType_ShouldReturnTrue_ForNullableReferenceType()
+    {
+        // Arrange
+        MethodInfo method = typeof(TestClass).GetMethod(nameof(TestClass.MethodWithNullability))!;
+        ParameterInfo nullableParameter = method.GetParameters().First(p => p.Name == "nullable");
+
+        // Act
+        bool result = nullableParameter.IsNullableReferenceType();
+
+        // Assert
+        await Assert.That(result).IsTrue().Because("Expected parameter 'nullable' to be recognized as a nullable reference type.");
+    }
+
+    [Test]
+    public async Task IsNullableReferenceType_ShouldReturnFalse_ForNonNullableReferenceType()
+    {
+        // Arrange
+        MethodInfo method = typeof(TestClass).GetMethod(nameof(TestClass.MethodWithNullability))!;
+        ParameterInfo nonNullableParameter = method.GetParameters().First(p => p.Name == "nonNullable");
+
+        // Act
+        bool result = nonNullableParameter.IsNullableReferenceType();
+
+        // Assert
+        await Assert.That(result).IsFalse().Because("Expected parameter 'nonNullable' to be recognized as a non-nullable reference type.");
+    }
+
+    [Test]
+    public async Task IsNullableReferenceType_ShouldReturnFalse_ForValueType()
+    {
+        // Arrange
+        MethodInfo method = typeof(TestClass).GetMethod(nameof(TestClass.MethodWithNullability))!;
+        ParameterInfo valueTypeParameter = method.GetParameters().First(p => p.Name == "valueType");
+
+        // Act
+        bool result = valueTypeParameter.IsNullableReferenceType();
+
+        // Assert
+        await Assert.That(result).IsFalse().Because("Expected parameter 'valueType' to be recognized as a non-nullable reference type.");
+    }
+
+}