How do you do a deep copy of an object in NET

Question

I want a true deep copy  In Java  this was easy  but how do you do it in C

User · Answer

The MSDN documentation seems to hint that Clone should perform a deep copy, but it is never explicitly stated:

The ICloneable interface contains one member, Clone, which is intended to support cloning beyond that supplied by MemberWiseClone… The MemberwiseClone method creates a shallow copy…

You can find my post helpful.

http://pragmaticcoding.com/index.php/cloning-objects-in-c/

User · Answer

I have a simpler idea  Use LINQ with a new selection   public class Fruit     public string Name  get  set     public int SeedCount  get  set      void SomeMethod       List lt Fruit gt  originalFruits   new List lt Fruit gt       originalFruits Add new Fruit  Name  Apple   SeedCount 10      originalFruits Add new Fruit  Name  Banana   SeedCount 0         Deep Copy   List lt Fruit gt  deepCopiedFruits   from f in originalFruits               select new Fruit  Name f Name  SeedCount f SeedCount

User · Answer

I wrote a deep object copy extension method  based on recursive  MemberwiseClone   It is fast  three times faster than BinaryFormatter   and it works with any object  You don t need a default constructor or serializable attributes   Source code   using System Collections Generic  using System Reflection  using System ArrayExtensions   namespace System       public static class ObjectExtensions               private static readonly MethodInfo CloneMethod   typeof Object  GetMethod  MemberwiseClone   BindingFlags NonPublic   BindingFlags Instance            public static bool IsPrimitive this Type type                        if  type    typeof String   return true              return  type IsValueType  amp  type IsPrimitive                      public static Object Copy this Object originalObject                        return InternalCopy originalObject  new Dictionary lt Object  Object gt  new ReferenceEqualityComparer                        private static Object InternalCopy Object originalObject  IDictionary lt Object  Object gt  visited                        if  originalObject    null  return null              var typeToReflect   originalObject GetType                if  IsPrimitive typeToReflect   return originalObject              if  visited ContainsKey originalObject   return visited originalObject               if  typeof Delegate  IsAssignableFrom typeToReflect   return null              var cloneObject   CloneMethod Invoke originalObject  null               if  typeToReflect IsArray                                var arrayType   typeToReflect GetElementType                    if  IsPrimitive arrayType     false                                        Array clonedArray    Array cloneObject                      clonedArray ForEach  array  indices    gt  array SetValue InternalCopy clonedArray GetValue indices   visited   indices                                                 visited Add originalObject  cloneObject               CopyFields originalObject  visited  cloneObject  typeToReflect               RecursiveCopyBaseTypePrivateFields originalObject  visited  cloneObject  typeToReflect               return cloneObject                     private static void RecursiveCopyBaseTypePrivateFields object originalObject  IDictionary lt object  object gt  visited  object cloneObject  Type typeToReflect                        if  typeToReflect BaseType    null                                RecursiveCopyBaseTypePrivateFields originalObject  visited  cloneObject  typeToReflect BaseType                   CopyFields originalObject  visited  cloneObject  typeToReflect BaseType  BindingFlags Instance   BindingFlags NonPublic  info   gt  info IsPrivate                                    private static void CopyFields object originalObject  IDictionary lt object  object gt  visited  object cloneObject  Type typeToReflect  BindingFlags bindingFlags   BindingFlags Instance   BindingFlags NonPublic   BindingFlags Public   BindingFlags FlattenHierarchy  Func lt FieldInfo  bool gt  filter   null                        foreach  FieldInfo fieldInfo in typeToReflect GetFields bindingFlags                                 if  filter    null  amp  amp  filter fieldInfo     false  continue                  if  IsPrimitive fieldInfo FieldType   continue                  var originalFieldValue   fieldInfo GetValue originalObject                   var clonedFieldValue   InternalCopy originalFieldValue  visited                   fieldInfo SetValue cloneObject  clonedFieldValue                                   public static T Copy lt T gt  this T original                        return  T Copy  Object original                        public class ReferenceEqualityComparer   EqualityComparer lt Object gt                public override bool Equals object x  object y                        return ReferenceEquals x  y                     public override int GetHashCode object obj                        if  obj    null  return 0              return obj GetHashCode                         namespace ArrayExtensions               public static class ArrayExtensions                       public static void ForEach this Array array  Action lt Array  int   gt  action                                if  array LongLength    0  return                  ArrayTraverse walker   new ArrayTraverse array                   do action array  walker Position                   while  walker Step                                      internal class ArrayTraverse                       public int   Position              private int   maxLengths               public ArrayTraverse Array array                                maxLengths   new int array Rank                   for  int i   0  i  lt  array Rank    i                                        maxLengths i    array GetLength i  - 1                                    Position   new int array Rank                              public bool Step                                 for  int i   0  i  lt  Position Length    i                                        if  Position i   lt  maxLengths i                                                 Position i                             for  int j   0  j  lt  i  j                                                          Position j    0                                                    return true                                                          return false

User · Answer

You can use Nested MemberwiseClone to do a deep copy  Its almost the same speed as copying a value struct  and its an order of magnitude faster than  a  reflection or  b  serialization  as described in other answers on this page    Note that if you use Nested MemberwiseClone for a deep copy  you have to manually implement a ShallowCopy for each nested level in the class  and a DeepCopy which calls all said ShallowCopy methods to create a complete clone  This is simple  only a few lines in total  see the demo code below   Here is the output of the code showing the relative performance difference  4 77 seconds for deep nested MemberwiseCopy vs  39 93 seconds for Serialization   Using nested MemberwiseCopy is almost as fast as copying a struct  and copying a struct is pretty darn close to the theoretical maximum speed  NET is capable of  which is probably quite close to the speed of the same thing in C or C    but would have to run some equivalent benchmarks to check this claim        Demo of shallow and deep copy  using classes and MemberwiseClone        Create Bob         Bob Age 30  Bob Purchase Description Lamborghini       Clone Bob  gt  gt  BobsSon       Adjust BobsSon details         BobsSon Age 2  BobsSon Purchase Description Toy car       Proof of deep copy  If BobsSon is a true clone  then adjusting BobsSon details will not affect Bob          Bob Age 30  Bob Purchase Description Lamborghini       Elapsed time  00 00 04 7795670 30000000     Demo of shallow and deep copy  using structs and value copying        Create Bob         Bob Age 30  Bob Purchase Description Lamborghini       Clone Bob  gt  gt  BobsSon       Adjust BobsSon details          BobsSon Age 2  BobsSon Purchase Description Toy car       Proof of deep copy  If BobsSon is a true clone  then adjusting BobsSon details will not affect Bob          Bob Age 30  Bob Purchase Description Lamborghini       Elapsed time  00 00 01 0875454 30000000     Demo of deep copy  using class and serialize deserialize        Elapsed time  00 00 39 9339425 30000000   To understand how to do a deep copy using MemberwiseCopy  here is the demo project      Nested MemberwiseClone example      Added to demo how to deep copy a reference class   Serializable     Not required if using MemberwiseClone  only used for speed comparison using serialization  public class Person       public Person int age  string description                this Age   age          this Purchase Description   description             Serializable     Not required if using MemberwiseClone     public class PurchaseType               public string Description          public PurchaseType ShallowCopy                         return  PurchaseType this MemberwiseClone                        public PurchaseType Purchase   new PurchaseType        public int Age         Add this if using nested MemberwiseClone         This is a class  which is a reference type  so cloning is more difficult      public Person ShallowCopy                 return  Person this MemberwiseClone                 Add this if using nested MemberwiseClone         This is a class  which is a reference type  so cloning is more difficult      public Person DeepCopy                        Clone the root             Person other    Person  this MemberwiseClone                       then clone the nested class          other Purchase   this Purchase ShallowCopy            return other             Added to demo how to copy a value struct  this is easy - a deep copy happens by default  public struct PersonStruct       public PersonStruct int age  string description                this Age   age          this Purchase Description   description            public struct PurchaseType               public string Description            public PurchaseType Purchase      public int Age         This is a struct  which is a value type  so everything is a clone by default      public PersonStruct ShallowCopy                 return  PersonStruct this               This is a struct  which is a value type  so everything is a clone by default      public PersonStruct DeepCopy                 return  PersonStruct this             Added only for a speed comparison  public class MyDeepCopy       public static T DeepCopy lt T gt  T obj                object result   null          using  var ms   new MemoryStream                          var formatter   new BinaryFormatter                formatter Serialize ms  obj               ms Position   0              result    T formatter Deserialize ms               ms Close                      return  T result            Then  call the demo from main       void MyMain string   args                              Console Write  Demo of shallow and deep copy  using classes and MemberwiseCopy  n                var Bob   new Person 30   Lamborghini                Console Write    Create Bob n                Console Write      Bob Age  0   Bob Purchase Description  1  n   Bob Age  Bob Purchase Description               Console Write    Clone Bob  gt  gt  BobsSon n                var BobsSon   Bob DeepCopy                Console Write    Adjust BobsSon details n                BobsSon Age   2              BobsSon Purchase Description    Toy car               Console Write      BobsSon Age  0   BobsSon Purchase Description  1  n   BobsSon Age  BobsSon Purchase Description               Console Write    Proof of deep copy  If BobsSon is a true clone  then adjusting BobsSon details will not affect Bob  n                Console Write      Bob Age  0   Bob Purchase Description  1  n   Bob Age  Bob Purchase Description               Debug Assert Bob Age    30               Debug Assert Bob Purchase Description     Lamborghini                var sw   new Stopwatch                sw Start                int total   0              for  int i   0  i  lt  100000  i                                  var n   Bob DeepCopy                    total    n Age                            Console Write    Elapsed time   0   1  n   sw Elapsed  total                                                  Console Write  Demo of shallow and deep copy  using structs  n                var Bob   new PersonStruct 30   Lamborghini                Console Write    Create Bob n                Console Write      Bob Age  0   Bob Purchase Description  1  n   Bob Age  Bob Purchase Description               Console Write    Clone Bob  gt  gt  BobsSon n                var BobsSon   Bob DeepCopy                Console Write    Adjust BobsSon details  n                BobsSon Age   2              BobsSon Purchase Description    Toy car               Console Write      BobsSon Age  0   BobsSon Purchase Description  1  n   BobsSon Age  BobsSon Purchase Description               Console Write    Proof of deep copy  If BobsSon is a true clone  then adjusting BobsSon details will not affect Bob  n                Console Write      Bob Age  0   Bob Purchase Description  1  n   Bob Age  Bob Purchase Description                               Debug Assert Bob Age    30               Debug Assert Bob Purchase Description     Lamborghini                var sw   new Stopwatch                sw Start                int total   0              for  int i   0  i  lt  100000  i                                  var n   Bob DeepCopy                    total    n Age                            Console Write    Elapsed time   0   1  n   sw Elapsed  total                                   Console Write  Demo of deep copy  using class and serialize deserialize  n                int total   0              var sw   new Stopwatch                sw Start                var Bob   new Person 30   Lamborghini                for  int i   0  i  lt  100000  i                                  var BobsSon   MyDeepCopy DeepCopy lt Person gt  Bob                   total    BobsSon Age                            Console Write    Elapsed time   0   1  n   sw Elapsed  total                     Console ReadKey            Again  note that if you use Nested MemberwiseClone for a deep copy  you have to manually implement a ShallowCopy for each nested level in the class  and a DeepCopy which calls all said ShallowCopy methods to create a complete clone  This is simple  only a few lines in total  see the demo code above   Note that when it comes to cloning an object  there is is a big difference between a  struct  and a  class     If you have a  struct   it s a value type so you can just copy it  and the contents will be cloned  If you have a  class   it s a reference type  so if you copy it  all you are doing is copying the pointer to it  To create a true clone  you have to be more creative  and use a method which creates another copy of the original object in memory  Cloning objects incorrectly can lead to very difficult-to-pin-down bugs  In production code  I tend to implement a checksum to double check that the object has been cloned properly  and hasn t been corrupted by another reference to it  This checksum can be switched off in Release mode  I find this method quite useful  often  you only want to clone parts of the object  not the entire thing  It s also essential for any use case where you are modifying objects  then feeding the modified copies into a queue    Update  It s probably possible to use reflection to recursively walk through the object graph to do a deep copy  WCF uses this technique to serialize an object  including all of its children  The trick is to annotate all of the child objects with an attribute that makes it discoverable  You might lose some performance benefits  however   Update  Quote on independent speed test  see comments below       I ve run my own speed test using Neil s serialize deserialize   extension method  Contango s Nested MemberwiseClone  Alex Burtsev s   reflection-based extension method and AutoMapper  1 million times   each  Serialize-deserialize was slowest  taking 15 7 seconds  Then   came AutoMapper  taking 10 1 seconds  Much faster was the   reflection-based method which took 2 4 seconds  By far the fastest was   Nested MemberwiseClone  taking 0 1 seconds  Comes down to performance   versus hassle of adding code to each class to clone it  If performance   isn t an issue go with Alex Burtsev s method         Simon Tewsi

User · Answer

The best way is       public interface IDeepClonable lt T gt  where T   class               T DeepClone               public class MyObj   IDeepClonable lt MyObj gt                public MyObj Clone                         var myObj   new MyObj                myObj  field1    field1   value type             myObj  field2    field2   value type             myObj  field3    field3   value type              if   child    null                                myObj  child    child DeepClone      reference type  DeepClone   that does the same                            int len    array Length              myObj  array   new MyObj len      array   collection             for  int i   0  i  lt  len  i                                  myObj  array i     array i                              return myObj                     private bool  field1          public bool Field1                       get   return  field1                set    field1   value                       private int  field2          public int Property2                       get   return  field2                set    field2   value                       private string  field3          public string Property3                       get   return  field3                set    field3   value                       private MyObj  child          private MyObj Child                       get   return  child                set    child   value                       private MyObj    array   new MyObj 4

User · Answer

public static object CopyObject object input                if  input    null                        object result   Activator CreateInstance input GetType                 foreach  FieldInfo field in input GetType   GetFields Consts AppConsts FullBindingList                                 if  field FieldType GetInterface  IList   false     null                                        field SetValue result  field GetValue input                                      else                                       IList listObject    IList field GetValue result                       if  listObject    null                                                foreach  object item in   IList field GetValue input                                                          listObject Add CopyObject item                                                                                                return result                    else                       return null                    This way is a few times faster than BinarySerialization AND this does not require the  Serializable  attribute

User · Answer

You can try this      public static object DeepCopy object obj                if  obj    null              return null          Type type   obj GetType             if  type IsValueType    type    typeof string                         return obj                    else if  type IsArray                        Type elementType   Type GetType                   type FullName Replace       string Empty                var array   obj as Array              Array copied   Array CreateInstance elementType  array Length               for  int i   0  i  lt  array Length  i                                  copied SetValue DeepCopy array GetValue i    i                             return Convert ChangeType copied  obj GetType                       else if  type IsClass                         object toret   Activator CreateInstance obj GetType                 FieldInfo   fields   type GetFields BindingFlags Public                           BindingFlags NonPublic   BindingFlags Instance               foreach  FieldInfo field in fields                                object fieldValue   field GetValue obj                   if  fieldValue    null                      continue                  field SetValue toret  DeepCopy fieldValue                              return toret                    else             throw new ArgumentException  Unknown type            Thanks to DetoX83 article on code project

User · Answer

I believe that the BinaryFormatter approach is relatively slow  which came as a surprise to me    You might be able to use ProtoBuf  NET for some objects if they meet the requirements of ProtoBuf  From the ProtoBuf Getting Started page  http   code google com p protobuf-net wiki GettingStarted    Notes on types supported   Custom classes that    Are marked as data-contract Have a parameterless constructor For Silverlight  are public Many common primitives  etc  Single dimension arrays  T   List lt T    IList lt T  Dictionary lt TKey  TValue    IDictionary lt TKey  TValue  any type which implements IEnumerable lt T  and has an Add T  method   The code assumes that types will be mutable around the elected members  Accordingly  custom structs are not supported  since they should be immutable   If your class meets these requirements you could try   public static void deepCopy lt T gt  ref T object2Copy  ref T objectCopy        using  var stream   new MemoryStream                  Serializer Serialize stream  object2Copy           stream Position   0          objectCopy   Serializer Deserialize lt T gt  stream             Which is VERY fast indeed     Edit   Here is working code for a modification of this  tested on  NET 4 6   It uses System Xml Serialization and System IO  No need to mark classes as serializable   public void DeepCopy lt T gt  ref T object2Copy  ref T objectCopy        using  var stream   new MemoryStream                  var serializer   new XS XmlSerializer typeof T             serializer Serialize stream  object2Copy           stream Position   0          objectCopy    T serializer Deserialize stream

User · Answer

I ve seen a few different approaches to this  but I use a generic utility method as such       public static T DeepClone lt T gt  this T obj     using  var ms   new MemoryStream          var formatter   new BinaryFormatter       formatter Serialize ms  obj      ms Position   0      return  T  formatter Deserialize ms          Notes    Your class MUST be marked as  Serializable  for this to work    Your source file must include the following code   using System Runtime Serialization Formatters Binary  using System IO

User · Answer

Maybe you only need a shallow copy  in that case use Object MemberWiseClone     There are good recommendations in the documentation for MemberWiseClone   for strategies to deep copy  -  http   msdn microsoft com en-us library system object memberwiseclone aspx

User · Answer

Building on Kilhoffer s solution     With C  3 0 you can create an extension method as follows   public static class ExtensionMethods          Deep clone     public static T DeepClone lt T gt  this T a                using  MemoryStream stream   new MemoryStream                          BinaryFormatter formatter   new BinaryFormatter                formatter Serialize stream  a               stream Position   0              return  T  formatter Deserialize stream                       which extends any class that s been marked as  Serializable  with a DeepClone method  MyClass copy   obj DeepClone

[c#] How do you do a deep copy of an object in .NET?

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