[FastClonerShallow]

Author: lofcz

README.md

@@ -84,6 +84,30 @@ TestPropsWithIgnored original = new TestPropsWithIgnored { A = 42, B = "Test val
 TestPropsWithIgnored clone = original.DeepClone(); // clone.B is null (default value of a given type)
 ```
 
+### Shallow Cloning Members
+
+When you need to copy a reference directly without deep cloning its contents, use `[FastClonerShallow]`.
+
+```csharp
+public class TreeNode
+{
+    public string Name { get; set; }
+    
+    [FastClonerShallow] // <-- reference copied directly
+    public TreeNode Parent { get; set; }
+    
+    public List<TreeNode> Children { get; set; }
+}
+
+TreeNode child = new TreeNode { 
+    Name = "Child", 
+    Parent = new TreeNode { Name = "Root" } 
+};
+TreeNode clone = child.DeepClone();
+```
+
+This differs from `[FastClonerIgnore]` which leaves the member as `null`/default. With `[FastClonerShallow]`, the original reference is preserved.
+
 You might also need to exclude certain types from ever being cloned. To do that, put offending types on a blacklist:
 ```cs
 FastCloner.FastCloner.IgnoreType(typeof(PropertyChangedEventHandler)); // or FastCloner.FastCloner.IgnoreTypes([ .. ])

src/FastCloner.SourceGenerator/ImplicitTypeAnalyzer.cs

@@ -103,7 +103,8 @@ bool TryHandleComponent(ITypeSymbol componentType, out MemberModel? componentMem
                             IsNullable: false,
                             HasGetter: true,
                             HasSetter: true,
-                            SetterIsAccessible: true
+                            SetterIsAccessible: true,
+                            IsShallowClone: false
                         );
                         return true;
                     }

src/FastCloner.SourceGenerator/MemberCloneGenerator.cs

@@ -18,6 +18,12 @@ public static string GetMemberAssignment(CloneGeneratorContext context, MemberMo
             case { IsProperty: true, HasGetter: true, HasSetter: false, IsInitOnly: false }:
                 return string.Empty;
             default:
+                // Handle shallow clone - direct reference copy (before checking TypeKind)
+                if (member.IsShallowClone)
+                {
+                    return $"{memberName} = {sourceVar}.{memberName}";
+                }
+                
                 switch (member.TypeKind)
                 {
                     case MemberTypeKind.Safe:
@@ -118,6 +124,13 @@ public static void WriteMemberCloning(CloneGeneratorContext context, MemberModel
                 WriteGetterOnlyCollectionPopulation(context, member, resultVar, sourceVar, stateVar);
                 return;
             default:
+                // Handle shallow clone - direct reference copy (before checking TypeKind)
+                if (member.IsShallowClone)
+                {
+                    sb.AppendLine($"            {resultVar}.{memberName} = {sourceVar}.{memberName};");
+                    return;
+                }
+                
                 switch (member.TypeKind)
                 {
                     case MemberTypeKind.Safe:

src/FastCloner.SourceGenerator/MemberCollector.cs

@@ -48,7 +48,8 @@ public static List<MemberAnalysis> GetMembers(
                         {
                             if (!HasIgnoreAttribute(property, compilation))
                             {
-                                members.Add(new MemberAnalysis(MemberModel.Create(property, nullabilityEnabled, compilation), property.Type));
+                                bool isShallow = HasShallowAttribute(property, compilation);
+                                members.Add(new MemberAnalysis(MemberModel.Create(property, nullabilityEnabled, compilation, isShallow), property.Type));
                             }
                         }
                     }
@@ -59,7 +60,8 @@ public static List<MemberAnalysis> GetMembers(
 
                     if (!HasIgnoreAttribute(field, compilation))
                     {
-                        members.Add(new MemberAnalysis(MemberModel.Create(field, nullabilityEnabled, compilation), field.Type));
+                        bool isShallow = HasShallowAttribute(field, compilation);
+                        members.Add(new MemberAnalysis(MemberModel.Create(field, nullabilityEnabled, compilation, isShallow), field.Type));
                     }
                 }
             }
@@ -161,4 +163,21 @@ private static bool HasIgnoreAttribute(ISymbol member, Compilation compilation)
 
         return false;
     }
+
+    private static bool HasShallowAttribute(ISymbol member, Compilation compilation)
+    {
+        INamedTypeSymbol? shallowAttribute = compilation.GetTypeByMetadataName("FastCloner.Code.FastClonerShallowAttribute");
+        if (shallowAttribute == null)
+            return false;
+
+        foreach (AttributeData? attr in member.GetAttributes())
+        {
+            if (SymbolEqualityComparer.Default.Equals(attr.AttributeClass, shallowAttribute))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }

src/FastCloner.SourceGenerator/MemberModel.cs

@@ -82,10 +82,11 @@ internal readonly record struct MemberModel(
     // Property accessor capabilities
     bool HasGetter,                  // Whether the property has a getter
     bool HasSetter,                  // Whether the property has a setter (regular, not init-only)
-    bool SetterIsAccessible          // Whether the setter is publicly accessible (not private/protected)
+    bool SetterIsAccessible,         // Whether the setter is publicly accessible (not private/protected)
+    bool IsShallowClone              // Whether the member should be shallow cloned (has [FastClonerShallow] attribute)
 ) : IEquatable<MemberModel>
 {
-    public static MemberModel Create(IPropertySymbol property, bool nullabilityEnabled, Compilation compilation)
+    public static MemberModel Create(IPropertySymbol property, bool nullabilityEnabled, Compilation compilation, bool isShallowClone = false)
     {
         (MemberTypeKind typeKind, string? elementName, string? keyName, string? valueName, bool elementSafe, bool elementClonable, bool keySafe, bool keyClonable, bool valSafe, bool valClonable, bool requiresFastCloner, CollectionKind collectionKind, string? concreteType, int arrayRank) 
             = AnalyzeType(property.Type, compilation);
@@ -130,10 +131,11 @@ public static MemberModel Create(IPropertySymbol property, bool nullabilityEnabl
             isNullable,
             hasGetter,
             hasSetter,
-            setterIsAccessible);
+            setterIsAccessible,
+            isShallowClone);
     }
 
-    public static MemberModel Create(IFieldSymbol field, bool nullabilityEnabled, Compilation compilation)
+    public static MemberModel Create(IFieldSymbol field, bool nullabilityEnabled, Compilation compilation, bool isShallowClone = false)
     {
         (MemberTypeKind typeKind, string? elementName, string? keyName, string? valueName, bool elementSafe, bool elementClonable, bool keySafe, bool keyClonable, bool valSafe, bool valClonable, bool requiresFastCloner, CollectionKind collectionKind, string? concreteType, int arrayRank) 
             = AnalyzeType(field.Type, compilation);
@@ -172,7 +174,8 @@ public static MemberModel Create(IFieldSymbol field, bool nullabilityEnabled, Co
             isNullable,
             hasGetter,
             hasSetter,
-            setterIsAccessible);
+            setterIsAccessible,
+            isShallowClone);
     }
 
     private static (MemberTypeKind kind, string? elem, string? key, string? val, bool elemSafe, bool elemClon, bool keySafe, bool keyClon, bool valSafe, bool valClon, bool requiresFastCloner, CollectionKind collKind, string? concreteType, int arrayRank) 

src/FastCloner.SourceGenerator/NestedTypeCollector.cs

@@ -83,7 +83,8 @@ public static void Collect(
                     false, // IsNullable
                     true,  // HasGetter - helper methods always have access
                     true,  // HasSetter - helper methods always have access
-                    true   // SetterIsAccessible - helper methods always have access
+                    true,  // SetterIsAccessible - helper methods always have access
+                    false  // IsShallowClone - helper methods are never shallow
                  );
 
                  if (!nestedTypes.ContainsKey(model.TypeFullName))
@@ -140,7 +141,8 @@ public static void Collect(
                     false, // IsNullable
                     true,  // HasGetter - helper methods always have access
                     true,  // HasSetter - helper methods always have access
-                    true   // SetterIsAccessible - helper methods always have access
+                    true,  // SetterIsAccessible - helper methods always have access
+                    false  // IsShallowClone - helper methods are never shallow
                  );
 
                  if (!nestedTypes.ContainsKey(model.TypeFullName))