Object serialization

Create a set of data types based upon inheritance. Each data type or class should have a print command that displays the contents of an instance of that class to standard output. Create instances of each class in your inheritance hierarchy and display them to standard output. Write each of the objects to a file named objects.dat in binary form using serialization or marshalling. Read the file objects.dat and print the contents of each serialized object.

Object serialization
You are encouraged to solve this task according to the task description, using any language you may know.

Ada

This file contains the package specification containing the public definitions of the inheritance tree rooted at the type Message. Each type in the inheritance tree has its own print procedure. <lang ada>with Ada.Calendar; use Ada.Calendar;

package Messages is

  type Message is tagged record
     Timestamp : Time;
  end record;
 
  procedure Print(Item : Message);
  procedure Display(Item : Message'Class);

  type Sensor_Message is new Message with record
     Sensor_Id : Integer;
     Reading : Float;
  end record;
  
  procedure Print(Item : Sensor_Message);
  
  type Control_Message is new Message with record
     Actuator_Id : Integer;
     Command     : Float;
  end record;
 
  procedure Print(Item : Control_Message);
 

end Messages;</lang>

The next portion contains the implementation of the procedures defined in the package specification. <lang ada>with Ada.Text_Io; use Ada.Text_Io; with Ada.Integer_Text_Io; use Ada.Integer_Text_Io; with Ada.Float_Text_IO; use Ada.Float_Text_IO;

package body Messages is

  -----------
  -- Print --
  -----------

  procedure Print (Item : Message) is
     The_Year : Year_Number;
     The_Month : Month_Number;
     The_Day   : Day_Number;
     Seconds   : Day_Duration;
  begin
     Split(Date => Item.Timestamp, Year => The_Year,
        Month => The_Month, Day => The_Day, Seconds => Seconds);
        
     Put("Time Stamp:");
     Put(Item => The_Year, Width => 4);
     Put("-");
     Put(Item => The_Month, Width => 1);
     Put("-");
     Put(Item => The_Day, Width => 1);
     New_Line;
  end Print; 

  -----------
  -- Print --
  -----------

  procedure Print (Item : Sensor_Message) is
  begin
     Print(Message(Item));
     Put("Sensor Id: ");
     Put(Item => Item.Sensor_Id, Width => 1);
     New_Line;
     Put("Reading: ");
     Put(Item => Item.Reading, Fore => 1, Aft => 4, Exp => 0);
     New_Line;
  end Print;

  -----------
  -- Print --
  -----------

  procedure Print (Item : Control_Message) is
  begin
     Print(Message(Item));
     Put("Actuator Id: ");
     Put(Item => Item.Actuator_Id, Width => 1);
     New_Line;
     Put("Command: ");
     Put(Item => Item.Command, Fore => 1, Aft => 4, Exp => 0);
     New_Line;
  end Print; 

  -------------
  ---Display --
  -------------
 
  procedure Display(Item : Message'Class) is
  begin
     Print(Item);
  end Display;
  

end Messages;</lang>

The final section of code creates objects of the three message types and performs the printing, writing, and reading. The Ada attributes 'Class'Output serialize the object and write it to the specified stream. The 'Class'Input attributes call a function automatically provided by the compiler which reads from the specified stream file and returns the object read. The Display procedure takes an object in the inheritance tree rooted at Message and dispatches the correct print procedure.

<lang ada>with Messages; use Messages; with Ada.Streams.Stream_Io; use Ada.Streams.Stream_Io; with Ada.Calendar; use Ada.Calendar; with Ada.Text_Io;

procedure Streams_Example is

  S1 : Sensor_Message;
  M1 : Message;
  C1 : Control_Message;
  Now : Time := Clock;
  The_File : Ada.Streams.Stream_Io.File_Type;
  The_Stream : Ada.Streams.Stream_IO.Stream_Access;

begin

  S1 := (Now, 1234, 0.025);
  M1.Timestamp := Now;
  C1 := (Now, 15, 0.334);
  Display(S1);
  Display(M1);
  Display(C1);
  begin
     Open(File => The_File, Mode => Out_File,
        Name => "Messages.dat");
  exception
     when others =>
        Create(File => The_File, Name => "Messages.dat");
  end;
  The_Stream := Stream(The_File);
  Sensor_Message'Class'Output(The_Stream, S1);
  Message'Class'Output(The_Stream, M1);
  Control_Message'Class'Output(The_Stream, C1);
  Close(The_File);
  Open(File => The_File, Mode => In_File,
     Name => "Messages.dat");
  The_Stream := Stream(The_File);
  Ada.Text_Io.New_Line(2);
  while not End_Of_File(The_File) loop
     Display(Message'Class'Input(The_Stream));
  end loop;
  Close(The_File);

end Streams_Example;</lang> Output results:

Time Stamp:2007-3-9
Sensor Id: 1234
Reading: 0.0250
Time Stamp:2007-3-9
Time Stamp:2007-3-9
Actuator Id: 15
Command: 0.3340
 

Time Stamp:2007-3-9
Sensor Id: 1234
Reading: 0.0250
Time Stamp:2007-3-9
Time Stamp:2007-3-9
Actuator Id: 15
Command: 0.3340

ALGOL 68

Translation of: python

Serialization in ALGOL 68 is achieved through a technique called straightening. <lang algol68>MODE ENTITY = STRUCT([6]CHAR name, INT creation); FORMAT entity repr = $"Name: "g", Created:"g$; MODE PERSON = STRUCT(ENTITY entity, STRING email); FORMAT person repr = $f(entity repr)", Email: "g$;

PERSON instance1 := PERSON(ENTITY("Cletus", 20080808), "test+1@localhost.localdomain"); print((name OF entity OF instance1, new line));

ENTITY instance2 := ENTITY("Entity",20111111); print((name OF instance2, new line));

FILE target; INT errno := open(target, "rows.dat", stand back channel); # open file #

1. Serialise #

put(target,(instance1, new line, instance2, new line)); printf(($"Serialised..."l$));

close(target); # flush file stream # errno := open(target, "rows.dat", stand back channel); # load again #

1. Unserialise #

PERSON i1; ENTITY i2; get(target,(i1, new line, i2, new line)); printf(($"Unserialised..."l$));

printf((person repr, i1, $l$)); printf((entity repr, i2, $l$))</lang> flexible length arrays (including strings), and tagged-union types are problematic as the lengths of the arrays, and the tag of the union is not stored in the file. Sometimes a format can be manually created to handle these lengths and tags. Also note that ALGOL 68 is strongly typed and the type (mode) of the objects not stored, but compiled into the code itself.

Output:

Cletus
Entity
Serialised...
Unserialised...
Name: Cletus, Created:  +20080808, Email: test+1@localhost.localdomain
Name: Entity, Created:  +20111111

C++

compiled with g++ -lboost_serialization serializationtest3.cpp -o serializationtest3

<lang cpp>#include <string>

1. include <fstream>
2. include <boost/serialization/string.hpp>
3. include <boost/archive/text_oarchive.hpp>
4. include <boost/archive/text_iarchive.hpp>
5. include <boost/serialization/base_object.hpp>
6. include <iostream>

class Employee { public :

  Employee( ) { }

  Employee ( const std::string &dep , const std::string &namen ) 
     : department( dep ) , name( namen ) {

my_id = count++ ;

     }

  std::string getName( ) const {
     return name ;
  }

  std::string getDepartment( ) const {
     return department ;
  }

  int getId( ) const {
     return my_id ;
  }

  void setDepartment( const std::string &dep ) {
     department.assign( dep ) ;
  }

  virtual void print( ) {
     std::cout << "Name: " << name << '\n' ;
     std::cout << "Id: " << my_id << '\n' ;
     std::cout << "Department: " << department << '\n' ;
  }

  virtual ~Employee( ) { } 
  static int count ;

private :

  std::string name ;
  std::string department ;
  int my_id ;
  friend class boost::serialization::access ;

  template <class Archive>
     void serialize( Archive &ar, const unsigned int version ) {

ar & my_id ; ar & name ; ar & department ;

     }

} ;

class Worker : public Employee { public :

  Worker( const std::string & dep, const std::string &namen ,

double hourlyPay ) : Employee( dep , namen ) , salary( hourlyPay) { }

  Worker( ) { }

  double getSalary( ) {
     return salary ;
  }

  void setSalary( double pay ) {
     if ( pay > 0 ) 

salary = pay ;

  }
  
  virtual void print( ) {
     Employee::print( ) ;
     std::cout << "wage per hour: " << salary << '\n' ;
  }

private :

  double salary ;
  friend class boost::serialization::access ;
  template <class Archive>
     void serialize ( Archive & ar, const unsigned int version ) {

ar & boost::serialization::base_object<Employee>( *this ) ; ar & salary ;

     }

} ;

int Employee::count = 0 ;

int main( ) {

  std::ofstream storefile( "/home/ulrich/objects.dat"  ) ; //creating objects of base class
  const Employee emp1( "maintenance" , "Fritz Schmalstieg"  ) ;
  const Employee emp2( "maintenance" , "John Berry" ) ;
  const Employee emp3( "repair" , "Pawel Lichatschow" ) ;
  const Employee emp4( "IT" , "Marian Niculescu" ) ;
  const Worker worker1( "maintenance" , "Laurent Le Chef" , 20 ) ;//creating objects of derived class
  const Worker worker2 ( "IT" , "Srinivan Taraman" , 55.35 ) ;
  boost::archive::text_oarchive oar ( storefile ) ;//starting serialization into designated file
  oar << emp1 ; 
  oar << emp2 ;
  oar << emp3 ;
  oar << emp4 ;
  oar << worker1 ;
  oar << worker2 ;
  storefile.close( ) ;
  std::cout << "Reading out the data again\n" ;
  Employee e1 , e2 , e3 , e4 ; //creating instances of base class objects for deserialization
  Worker w1, w2 ; // same for objects of derived class
  std::ifstream sourcefile( "/home/ulrich/objects.dat"  ) ;
  boost::archive::text_iarchive iar( sourcefile ) ;//starting deserialization
  iar >> e1 >> e2 >> e3 >> e4 ; 
  iar >> w1 >> w2 ;
  sourcefile.close( ) ;
  std::cout << "And here are the data after deserialization!( abridged):\n" ;
  e1.print( ) ;
  e3.print( ) ;
  w2.print( ) ;
  return 0 ;

}</lang> creating the following output:

Reading out the data again
And here are the data after deserialization!( abridged):
Name: Fritz Schmalstieg
Id: 0
Department: maintenance
Name: Pawel Lichatschow
Id: 2
Department: repair
Name: Srinivan Taraman
Id: 5
Department: IT
wage per hour: 55.35

C#

<lang csharp>using System; using System.IO; using System.Collections.Generic; using System.Runtime.Serialization.Formatters.Binary;

namespace Object_serialization {

 [Serializable] public class Being
 {
   public bool Alive { get; set; }
 }

 [Serializable] public class Animal: Being
 {
   public Animal() { }

   public Animal(long id, string name, bool alive = true)
   {
     Id = id;
     Name = name;
     Alive = alive;
   }

   public long Id { get; set; }
   public string Name { get; set; }

   public void Print() { Console.WriteLine("{0}, id={1} is {2}",
     Name, Id, Alive ? "alive" : "dead"); }
 }

 internal class Program
 {
   private static void Main()
   {
     string path = 
       Environment.GetFolderPath(Environment.SpecialFolder.Desktop)+"\\objects.dat";

     var n = new List<Animal>
             {
               new Animal(1, "Fido"),
               new Animal(2, "Lupo"),
               new Animal(7, "Wanda"),
               new Animal(3, "Kiki", alive: false)
             };

     foreach(Animal animal in n)
       animal.Print();

     using(var stream = new FileStream(path, FileMode.Create, FileAccess.Write))
       new BinaryFormatter().Serialize(stream, n);

     n.Clear();
     Console.WriteLine("---------------");
     List<Animal> m;

     using(var stream = new FileStream(path, FileMode.Open, FileAccess.Read))
       m = (List<Animal>) new BinaryFormatter().Deserialize(stream);

     foreach(Animal animal in m)
       animal.Print();
   }
 }

}</lang>

Fido, id=1 is alive
Lupo, id=2 is alive
Wanda, id=7 is alive
Kiki, id=3 is dead
---------------
Fido, id=1 is alive
Lupo, id=2 is alive
Wanda, id=7 is alive
Kiki, id=3 is dead

Caché ObjectScript

<lang cos>Class Serialize.Employee Extends %SerialObject {

Method %OnNew(ByRef pId As %Integer = 0, pDepartment As %String, pName As %String) As %Status { Do ..IDSet(pId) Set pId=pId+1 Do ..DepartmentSet(pDepartment) Do ..NameSet(pName) Quit $$$OK }

Method Print() { Write "[", ..%ClassName(), "]", ! Write "- ID: "_..IDGet(), ! Write "- Name: "_..NameGet(), ! Write "- Department: "_..DepartmentGet(), ! Quit }

Property ID As %Integer [ Private ]; Property Name As %String [ Private ]; Property Department As %String [ Private ];

}</lang>

<lang cos>Class Serialize.Worker Extends Employee {

Method %OnNew(ByRef pId As %Integer = 0, pDepartment As %String, pName As %String, pHourlyPay As %Numeric) As %Status { Do ..HourlyPaySet(pHourlyPay) Quit ##super(.pId, pDepartment, pName) }

Method Print() { Do ##super() Write "- Hourly Pay: ", $FNumber(..HourlyPayGet(), ",", 2), ! Quit }

Method HourlyPaySet(pHourlyPay As %Numeric) As %Status [ ServerOnly = 1 ] { Set i%HourlyPay=$Select(pHourlyPay<0: 0, 1: pHourlyPay) Quit $$$OK }

Property HourlyPay As %Numeric [ Private ];

}</lang>

<lang cos>Class Serialize.Example Extends %SerialObject {

ClassMethod Main() { Do ..Save("/temp/objects.dat") Do ..Load("/temp/objects.dat") Quit }

ClassMethod Save(pFilename As %String) { // creating objects of base class Set emp1 = ##class(Employee).%New(.id, "Maintenance", "Fritz Schmalstieg") Set emp2 = ##class(Employee).%New(.id, "Maintenance", "John Berry") Set emp3 = ##class(Employee).%New(.id, "Repair", "Pawel Lichatschow") Set emp4 = ##class(Employee).%New(.id, "IT", "Marian Niculescu")

// creating objects of derived class Set worker1 = ##class(Worker).%New(.id, "Maintenance", "Laurent Le Chef", 20) Set worker2 = ##class(Worker).%New(.id, "IT", "Srinivan Taraman", 55.35)

// put objects into collections Set example = ..%New() Set sc = example.Employees.Insert(emp1) Set sc = example.Employees.Insert(emp2) Set sc = example.Employees.Insert(emp3) Set sc = example.Employees.Insert(emp4) Set sc = example.Workers.Insert(worker1) Set sc = example.Workers.Insert(worker2)

// serialize the data and save to a file Set sc=example.%GetSwizzleObject(,.oid) Set fs=##class(%Stream.FileBinary).%New() Set fs.Filename=pFilename Set sc=fs.Write(oid) Set sc=fs.%Save() Quit }

ClassMethod Load(pFilename As %String) { // read serialized data from file Set fs=##class(%Stream.FileBinary).%New() Set fs.Filename=pFilename Set oid=fs.Read(.len, .sc)

// open the example object Set example = ..%Open(oid,, .sc) Do example.Employees.GetAt(1).Print() Do example.Employees.GetAt(3).Print() Do example.Workers.GetAt(2).Print() Quit }

Property Employees As list Of Employee; Property Workers As list Of Worker;

}</lang>

Examples:

USER>Do ##class(Serialize.Example).Main()
[Employee]
- ID: 0
- Name: Fritz Schmalstieg
- Department: Maintenance
[Employee]
- ID: 2
- Name: Pawel Lichatschow
- Department: Repair
[Worker]
- ID: 5
- Name: Srinivan Taraman
- Department: IT
- Hourly Pay: 55.35

Common Lisp

Library: cl-serializer

<lang lisp>(defmacro with-serialization-to-file ((stream pathname) &body body)

 `(with-open-file (,stream ,pathname
                           :element-type '(unsigned-byte 8)
                           :direction :output
                           :if-exists :supersede)
    ,@body))

(defclass entity ()

 ((name :initarg :name :initform "Some entity")))

(defclass person (entity)

 ((name :initarg :name :initform "The Nameless One")))</lang>

And now the REPL log:

<lang lisp>CL-USER> (list (make-instance 'entity)

              (make-instance 'person))

(#<ENTITY {1004B13141}> #<PERSON {1004B142B1}>) CL-USER> (mapc #'describe *)

1. <ENTITY {1004B13141}>

 [standard-object]

Slots with :INSTANCE allocation:

 NAME  = "Some entity"

1. <PERSON {1004B142B1}>

 [standard-object]

Slots with :INSTANCE allocation:

 NAME  = "The Nameless One"

(#<ENTITY {1004B13141}> #<PERSON {1004B142B1}>) CL-USER> (with-serialization-to-file (stream "/tmp/objects.dat")

          (cl-serializer:serialize * :output stream)
          ;; SERIALIZE shows an octet-vector as its return value
          (values))

No value

CL-USER> (mapc #'describe (with-open-file (stream "/tmp/objects.dat"

                                                 :element-type '(unsigned-byte 8))
                           (cl-serializer:deserialize stream)))

1. <ENTITY {1003C12911}>

 [standard-object]

Slots with :INSTANCE allocation:

 NAME  = "Some entity"

1. <PERSON {1003C12A81}>

 [standard-object]

Slots with :INSTANCE allocation:

 NAME  = "The Nameless One"

(#<ENTITY {1003C12911}> #<PERSON {1003C12A81}>)</lang>

D

Library: ProtocolBuffer

If the requirement was not for binary, the doost library would be a better fit for this task. First, create a file named test.proto with the following contents:

package test;
message base1 {
	  required int32 i32 = 1;
}
message base2 {
	  repeated base1 rep = 1;
}

Run "pbcompiler test.proto" to generate the serializable code. It should generate a D code file named test.d. In your main file, use the following code: <lang d>import test1; import std.stdio; import std.file; class full2:base2 {

       this(byte[]manip,bool isroot=true) {super(manip,isroot);}
       this(){super();}
       void print() {
               foreach(item;rep) {
                       writefln(item.i32);
               }
       }

}

void main() {

       full2 base = new full2();
       base1 tmp = new base1;
       tmp.i32 = 34;
       base.add_rep(tmp);
       tmp = new base1;
       tmp.i32 = 32;
       base.add_rep(tmp);
       tmp = new base1;
       tmp.i32 = 33;
       base.add_rep(tmp);
       tmp = new base1;
       tmp.i32 = 36;
       base.add_rep(tmp);
       writefln("Input data:");
       base.print;
       write("objects.dat",base.Serialize());
       byte[]filedata = cast(byte[])read("objects.dat");
       base = new full2(filedata);
       writefln("Output data:");
       base.print;

}</lang>

E

(Inheritance, while supported by various features and patterns, is not a preferred design component in E; nor are simple record data structures.)

<lang e>def makeEvent(time :int) {

   return def event {
       to __printOn(out) { out.print(`@@$time`) }
       to __optUncall() { return [makeEvent, "run", [time]] }
       to getTime() { return time }
   }

}

def makeArrival(time :int, what :any, position :int) {

   return def arrival extends makeEvent(time) {
       to __printOn(out) { 
           out.print(`$what to $position $super`)
       }
       to __optUncall() { 
           return [makeArrival, "run", [time, what, position]]
       }
     
       to getWhat() { return what }
       to getPosition() { return position }
   }

}</lang>

After defining our data types, we can prepare to serialize them.

<lang e>def surgeon := <import:org.erights.e.elib.serial.makeSurgeon>().diverge() surgeon.addExit(makeEvent, "makeEvent") surgeon.addExit(makeArrival, "makeArrival")</lang>

The 'exits' of the surgeon (so called because it cuts and joins object subgraphs) specify the points at which serialization should stop, instead replacing references to the objects with the specified names. On unserialization, the names are looked up and replaced with the corresponding objects. (The surgeon provides default exits for such things as false, true, null, and the list constructor.)

<lang e>def objs := [makeEvent(timer.now()),

            makeArrival(timer.now(), "Smith", 7)]

stdout.println(objs) <file:objects.dat>.setBytes(surgeon.serialize(objs)) stdout.println(surgeon.unserialize(<file:objects.dat>.getBytes()))</lang>

Erlang

Erlang is not object oriented. This code is based upon my understanding of the Algol 68 example above. <lang Erlang> -module( object_serialization ).

-export( [task/0] ).

-record( entity, {name, date} ). -record( person, {entity, email} ).

task() -> Person = #person{entity=#entity{name="Cletus", date=20080808}, email="test+1@localhost.localdomain"}, print( Person ), Entity = #entity{name="Entity", date=20111111}, print( Entity ), ok = file:write_file( "objects.dat", erlang:term_to_binary([Person, Entity]) ), {ok, Binary} = file:read_file( "objects.dat" ), [New_person, New_entity] = erlang:binary_to_term( Binary ), io:fwrite( "Deserialized\n" ), print( New_person ), print( New_entity ).

print( #entity{name=Name, date=Date} ) -> io:fwrite( "Entity: " ), io:fwrite( "name: ~p, date: ~p~n", [Name, Date] ); print( #person{entity=Entity, email=Email} ) -> io:fwrite( "Person: " ), print( Entity ), io:fwrite( "\temail: ~p~n", [Email] ). </lang>

Output:

<9> object_serialization:task().
Person: Entity: name: "Cletus", date: 20080808
        email: "test+1@localhost.localdomain"
Entity: name: "Entity", date: 20111111
Deserialized
Person: Entity: name: "Cletus", date: 20080808
        email: "test+1@localhost.localdomain"
Entity: name: "Entity", date: 20111111

Go

Go has a few choices for serialization. The method shown here is the native method, which is compact and type-aware.

A note on object oriented stuff, the object hierarchy required by the task description is implemented here with embedded structs. The polymorphism required by the task description is handled nicely with an interface. The functional polymorphism is orthogonal to the object hierarchy, not conflated with it. <lang go>package main

import (

   "encoding/gob"
   "fmt"
   "os"

)

type printable interface {

   print()

}

func main() {

   // create instances
   animals := []printable{
       &Animal{Alive: true},
       &Cat{},
       &Lab{
           Dog:   Dog{Animal: Animal{Alive: true}},
           Color: "yellow",
       },
       &Collie{Dog: Dog{
           Animal:           Animal{Alive: true},
           ObedienceTrained: true,
       }},
   }

   // display
   fmt.Println("created:")
   for _, a := range animals {
       a.print()
   }

   // serialize
   f, err := os.Create("objects.dat")
   if err != nil {
       fmt.Println(err)
       return
   }
   for _, a := range animals {
       gob.Register(a)
   }
   err = gob.NewEncoder(f).Encode(animals)
   if err != nil {
       fmt.Println(err)
       return
   }
   f.Close()

   // read
   f, err = os.Open("objects.dat")
   if err != nil {
       fmt.Println(err)
       return
   }
   var clones []printable
   gob.NewDecoder(f).Decode(&clones)
   if err != nil {
       fmt.Println(err)
       return
   }

   // display
   fmt.Println("\nloaded from objects.dat:")
   for _, c := range clones {
       c.print()
   }

}

type Animal struct {

   Alive bool

}

func (a *Animal) print() {

   if a.Alive {
       fmt.Println("   live animal, unspecified type")
   } else {
       fmt.Println("   dead animal, unspecified type")
   }

}

type Dog struct {

   Animal
   ObedienceTrained bool

}

func (d *Dog) print() {

   switch {
   case !d.Alive:
       fmt.Println("   dead dog")
   case d.ObedienceTrained:
       fmt.Println("   trained dog")
   default:
       fmt.Println("   dog, not trained")
   }

}

type Cat struct {

   Animal
   LitterBoxTrained bool

}

func (c *Cat) print() {

   switch {
   case !c.Alive:
       fmt.Println("   dead cat")
   case c.LitterBoxTrained:
       fmt.Println("   litter box trained cat")
   default:
       fmt.Println("   cat, not litter box trained")
   }

}

type Lab struct {

   Dog 
   Color string

}

func (l *Lab) print() {

   var r string
   if l.Color == "" {
       r = "lab, color unspecified"
   } else {
       r = l.Color + " lab"
   }
   switch {
   case !l.Alive:
       fmt.Println("   dead", r)
   case l.ObedienceTrained:
       fmt.Println("   trained", r)
   default:
       fmt.Printf("   %s, not trained\n", r)
   }

}

type Collie struct {

   Dog 
   CatchesFrisbee bool

}

func (c *Collie) print() {

   switch {
   case !c.Alive:
       fmt.Println("   dead collie")
   case c.ObedienceTrained && c.CatchesFrisbee:
       fmt.Println("   trained collie, catches frisbee")
   case c.ObedienceTrained && !c.CatchesFrisbee:
       fmt.Println("   trained collie, but doesn't catch frisbee")
   case !c.ObedienceTrained && c.CatchesFrisbee:
       fmt.Println("   collie, not trained, but catches frisbee")
   case !c.ObedienceTrained && !c.CatchesFrisbee:
       fmt.Println("   collie, not trained, doesn't catch frisbee")
   }

}</lang> Output:

created:
   live animal, unspecified type
   dead cat
   yellow lab, not trained
   trained collie, but doesn't catch frisbee

loaded from objects.dat:
   live animal, unspecified type
   dead cat
   yellow lab, not trained
   trained collie, but doesn't catch frisbee

Groovy

Sample Serializable Classes (borrowed from Java example. Sorta.): <lang groovy>class Entity implements Serializable {

   static final serialVersionUID = 3504465751164822571L
   String name = 'Thingamabob'
   public String toString() { return name }

}

class Person extends Entity implements Serializable {

   static final serialVersionUID = -9170445713373959735L
   Person() { name = 'Clement' }
   Person(name) { this.name = name }

}</lang>

Writing objects: <lang groovy>File objectStore = new File('objectStore.ser') if (objectStore.exists()) { objectStore.delete() } assert ! objectStore.exists() def os try {

   os = objectStore.newObjectOutputStream()
   os << new Person()
   os << 10.5
   os << new Person('Cletus')
   os << new Date()
   os << new Person('Pious')
   os << java.awt.Color.RED
   os << new Person('Linus')
   os << 'just random garbage'
   os << new Person('Lucy')
   os << ['lists', 'are', 'serializable']
   os << new Person('Schroeder')

} catch (e) { throw new Exception(e) } finally { os?.close() } assert objectStore.exists()</lang>

Reading objects: <lang groovy>def is try {

   is = objectStore.newObjectInputStream(this.class.classLoader)
   is.eachObject { println it }

} catch (e) { throw new Exception(e) } finally { is?.close() }

objectStore.delete() assert ! objectStore.exists()</lang>

Output:

Clement
10.5
Cletus
Wed Jan 18 02:07:29 CST 2012
Pious
java.awt.Color[r=255,g=0,b=0]
Linus
just random garbage
Lucy
[lists, are, serializable]
Schroeder

J

This should be sufficient for this task:

<lang j>lin_z_=:5!:5 serializeObject=:3 :0

 p=. copath y
 d=. ;LF;"1(,'=:';lin__y)"0 nl__y i.4
 '(',(5!:5<'p'),')(copath[cocurrent@])cocreate ,,d,LF

)

deserializeObject=:3 :0

 o=.conl 1
 0!:100 y
 (conl 1)-.o

)

coclass'room'

 create=:3 :'size=:y'
 print=:3 :'room size ,":size'

coclass'kitchen'

 coinsert'room'
 print=:3 :'kitchen size ,":size'

coclass'kitchenWithSink'

 coinsert'kitchen'
 print=:3 :'kitchen with sink size ,":size'

cocurrent'base'

R=:'small' conew 'room' K=:'medium' conew 'kitchen' S=:'large' conew 'kitchenWithSink' print__R print__K print__S

(;<@serializeObject"0 R,K,S) 1!:2 <'objects.dat'

'r1 k1 s1'=: <"0 deserializeObject 1!:1<'objects.dat' print__r1 print__k1 print__s1</lang>

Here is how the last part looks in action:

<lang j> print__R room size small

  print__K

kitchen size medium

  print__S

kitchen with sink size large

  (;<@serializeObject"0 R,K,S) 1!:2 <'objects.dat'
  
  'r1 k1 s1'=: <"0 deserializeObject 1!:1<'objects.dat'
  print__r1

room size small

  print__k1

kitchen size medium

  print__s1

kitchen with sink size large</lang>

Note also that J does not attempt to distinguish, at the language level, between an object reference and something that looks like an object reference but is not. This must be done at the application level, which in turn can create a variety of opportunities and/or burdens for the program designer.

Java

<lang java>import java.io.*;

// classes must implement java.io.Serializable in order to be serializable class Entity implements Serializable {

   // it is recommended to hard-code serialVersionUID so changes to class
   // will not invalidate previously serialized objects
   static final long serialVersionUID = 3504465751164822571L;
   String name = "Entity";
   public String toString() { return name; }

}

class Person extends Entity implements Serializable {

   static final long serialVersionUID = -9170445713373959735L;
   Person() { name = "Cletus"; }

}

public class SerializationTest {

   public static void main(String[] args) {
       Person instance1 = new Person();
       System.out.println(instance1);

       Entity instance2 = new Entity();
       System.out.println(instance2);

       // Serialize
       try {
           ObjectOutput out = new ObjectOutputStream(new FileOutputStream("objects.dat")); // open ObjectOutputStream

           out.writeObject(instance1); // serialize "instance1" and "instance2" to "out"
           out.writeObject(instance2);
           out.close();
           System.out.println("Serialized...");
       } catch (IOException e) {
           System.err.println("Something screwed up while serializing");
           e.printStackTrace();
           System.exit(1);
       }

       // Deserialize
       try {
           ObjectInput in = new ObjectInputStream(new FileInputStream("objects.dat")); // open ObjectInputStream

           Object readObject1 = in.readObject(); // read two objects from "in"
           Object readObject2 = in.readObject(); // you may want to cast them to the appropriate types
           in.close();
           System.out.println("Deserialized...");

           System.out.println(readObject1);
           System.out.println(readObject2);
       } catch (IOException e) {
           System.err.println("Something screwed up while deserializing");
           e.printStackTrace();
           System.exit(1);
       } catch (ClassNotFoundException e) {
           System.err.println("Unknown class for deserialized object");
           e.printStackTrace();
           System.exit(1);
       }
   }

}</lang>

Objective-C

Works with: GNUstep

Works with: Cocoa

About Cocoa, I can't test it, but I've used Apple's documentation to learn how to do it (see here; serializing or marshalling is rather known in Obj-C world as archiving).

There exists also a way of serializing without the GNUstep/Cocoa framework, using the runtime of Objective-C (so it could be slightly implementation dependent, see Serialization on Wikipedia). (I will work on it and will put here a full working example compatible with the task).

<lang objc>#import <Foundation/Foundation.h>

// a fantasy two level hierarchy @interface Animal : NSObject <NSCoding> {

 NSString *animalName;
 int numberOfLegs;

} - (id) initWithName: (NSString*)name andLegs: (NSInteger)legs; - (void) dump; // the following allows "(de)archiving" of the object - (void) encodeWithCoder: (NSCoder*)coder; - (id) initWithCoder: (NSCoder*)coder; @end

@implementation Animal - (id) initWithName: (NSString*)name andLegs: (NSInteger)legs {

 if ((self = [super init])) {
   animalName = [name retain];
   numberOfLegs = legs;
 }
 return self;

} - (void) dealloc {

 [animalName release];
 [super dealloc];

} - (void) dump {

 NSLog(@"%@ has %d legs", animalName, numberOfLegs);

} // ======== - (void) encodeWithCoder: (NSCoder*)coder {

 [coder encodeObject: animalName forKey: @"Animal.name"];
 [coder encodeInt: numberOfLegs forKey: @"Animal.legs"];

} - (id) initWithCoder: (NSCoder*)coder {

 if ((self = [super init])) {
   animalName = [[coder decodeObjectForKey: @"Animal.name"] retain];
   numberOfLegs = [coder decodeIntForKey: @"Animal.legs"];
 }
 return self;

} @end

@interface Mammal : Animal <NSCoding> {

 BOOL hasFur;
 NSMutableArray *eatenList;

} - (id) initWithName: (NSString*)name hasFur: (BOOL)fur; - (void) addEatenThing: (NSString*)thing; - (void) dump; // for archiving / dearchiving: - (void) encodeWithCoder: (NSCoder*)coder; - (id) initWithCoder: (NSCoder*)coder; @end

@implementation Mammal - (id) init {

 if ((self = [super init])) {
   hasFur = NO;
   eatenList = [[NSMutableArray alloc] initWithCapacity: 10];
 }
 return self;

} - (id) initWithName: (NSString*)name hasFur: (BOOL)fur {

 if ((self = [super initWithName: name andLegs: 4])) {
   hasFur = fur;
   eatenList = [[NSMutableArray alloc] initWithCapacity: 10];
 }
 return self;

} - (void) addEatenThing: (NSString*)thing {

 [eatenList addObject: thing];

} - (void) dealloc {

 [eatenList release];
 [super dealloc];

} - (void) dump {

 [super dump];
 NSLog(@"has fur? %@", (hasFur) ? @"yes" : @"no" );
 // fast enum not implemented yet in gcc 4.3, at least
 // without a patch that it seems to exist...
 NSEnumerator *en = [eatenList objectEnumerator];
 id element;
 NSLog(@"it has eaten %d things:", [eatenList count]);
 while( (element = [en nextObject]) != nil )
   NSLog(@"it has eaten a %@", element);
 NSLog(@"end of eaten things list");

} // ========= de/archiving - (void) encodeWithCoder: (NSCoder*)coder {

 [super encodeWithCoder: coder];
 [coder encodeBool: numberOfLegs forKey: @"Mammal.hasFur"];
 [coder encodeObject: eatenList forKey: @"Mammal.eaten"];

} - (id) initWithCoder: (NSCoder*)coder {

 if ((self = [super initWithCoder: coder])) {
   hasFur = [coder decodeBoolForKey: @"Mammal.hasFur"];
   eatenList = [[coder decodeObjectForKey: @"Mammal.eaten"] retain];
 }
 return self;

} @end

int main() {

 Mammal *aMammal;
 Animal *anAnimal;
 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 
 // let us create a fantasy animal
 anAnimal = [[Animal alloc]

initWithName: @"Eptohippos" andLegs: 7 ];

 // for some reason an Eptohippos is not an horse with 7 legs,
 // and it is not a mammal, of course...

 // let us create a fantasy mammal (which is an animal too)
 aMammal = [[Mammal alloc]

initWithName: @"Mammaluc" hasFur: YES ];

 // let us add some eaten stuff...
 [aMammal addEatenThing: @"lamb"];
 [aMammal addEatenThing: @"table"];
 [aMammal addEatenThing: @"web page"];

 // dump anAnimal
 NSLog(@"----- original Animal -----");
 [anAnimal dump];

 // dump aMammal...
 NSLog(@"----- original Mammal -----");
 [aMammal dump];

 // now let us store the objects...
 NSMutableData *data = [[NSMutableData alloc] init];
 NSKeyedArchiver *arch = [[NSKeyedArchiver alloc]

initForWritingWithMutableData: data];

 [arch encodeObject: anAnimal forKey: @"Eptohippos"];
 [arch encodeObject: aMammal forKey: @"Mammaluc"];
 [anAnimal release];
 [aMammal release];
 [arch finishEncoding];
 [arch release];
 [data writeToFile: @"objects.dat" atomically: YES];
 [data release];

 // now we want to retrieve the saved objects...
 NSData *ldata = [[NSData alloc]

initWithContentsOfFile: @"objects.dat"];

 NSKeyedUnarchived *darch = [[NSKeyedUnarchiver alloc]

initForReadingWithData: ldata];

 Animal *archivedAnimal = [darch decodeObjectForKey: @"Eptohippos"];
 Mammal *archivedMammal = [darch decodeObjectForKey: @"Mammaluc"];
 [darch finishDecoding];
 [ldata release];
 [darch release];

 // now let's dump/print the objects...
 NSLog(@"\n");
 NSLog(@"----- the archived Animal -----");
 [archivedAnimal dump];
 NSLog(@"----- the archived Mammal -----");
 [archivedMammal dump];

 [pool release];
 return EXIT_SUCCESS;

}</lang>

Objeck

<lang objeck> bundle Default {

 class Thingy {
   @id : Int;

   New(id : Int) {
     @id := id;
   }

   method : public : Print() ~ Nil {
     @id->PrintLine();
   }
 }

 class Person from Thingy {
   @name : String;

   New(id : Int, name : String) {
     Parent(id);
     @name := name;
   }

   method : public : Print() ~ Nil {
     @id->PrintLine();
     @name->PrintLine();
   }
 }

 class Serial {
   function : Main(args : String[]) ~ Nil {
     t := Thingy->New(7);
     p := Person->New(13, "Bush");

     s := IO.Serializer->New();
     s->Write(t->As(Base));
     s->Write(p->As(Base));

     writer := IO.FileWriter->New("objects.dat");
     writer->WriteBuffer(s->Serialize());
     writer->Close();

     buffer := IO.FileReader->ReadBinaryFile("objects.dat");
     d := IO.Deserializer->New(buffer);

     t2 := d->ReadObject()->As(Thingy);
     t2->Print();
     p2 := d->ReadObject()->As(Person);
     p2->Print();
   }
 }

} </lang>

OCaml

Objects which contain methods are difficult to serialize because it will want to serialize those methods too, but functions usually cannot be serialized. Instead, here we perform the task on non-object datatypes, with an outside function to print them.

<lang ocaml>type entity = { name : string }

let create_entity () = { name = "Entity" } let print_entity x = print_endline x.name let create_person () = { name = "Cletus" }

let instance1 = create_person () let instance2 = create_entity ()

(* Serialize *) let out_chan = open_out_bin "objects.dat";; output_value out_chan instance1;; output_value out_chan instance2;; close_out out_chan;;

(* Deserialize *) let in_chan = open_in_bin "objects.dat";; let result1 : entity = input_value in_chan;; let result2 : entity = input_value in_chan;; close_in in_chan;;

print_entity result1;; print_entity result2;;</lang>

Oz

Stateless values can easily be serialized with functions from the Pickle module. Objects are not stateless, though.

Some objects can be converted to a stateless chunk by using ObjectSupport.reflect. For technical reasons, this will only work for a small subset of classes.

For a general solution, see Object Serialization/Oz.

Perl

Library: Storable

<lang perl>{

   package Greeting;
   sub new {
       my $v = "Hello world!\n"; 
       bless \$v, shift;
   };
   sub stringify {
       ${shift()};
   };

}; {

   package Son::of::Greeting;
   use base qw(Greeting); # inherit methods
   sub new { # overwrite method of super class
       my $v = "Hello world from Junior!\n"; 
       bless \$v, shift;
   };

}; {

   use Storable qw(store retrieve);
   package main;
   my $g1 = Greeting->new;
   my $s1 = Son::of::Greeting->new;
   print $g1->stringify;
   print $s1->stringify;

   store $g1, 'objects.dat';
   my $g2 = retrieve 'objects.dat';

   store $s1, 'objects.dat';
   my $s2 = retrieve 'objects.dat';

   print $g2->stringify;
   print $s2->stringify;

};</lang>

Library: MooseX

The same, using MooseX to serialize to JSON. <lang perl>use MooseX::Declare;

class Greeting {

   use MooseX::Storage;
   with Storage('format' => 'JSON', io => 'File');
   has string => (is => 'ro', default => "Hello world!\n");

} class Son::Of::Greeting extends Greeting {

   has string => (is => 'ro', default => "Hello from Junior!\n");

}

my $g1 = Greeting->new; my $s1 = Son::Of::Greeting->new;

print $g1->string; print $s1->string;

$g1->store('object1.json'); my $g2 = Greeting->load('object1.json');

$s1->store('object2.json'); my $s2 = Son::Of::Greeting->load('object2.json');

print $g2->string; print $s2->string; </lang> This time the objects were serialized to the JSON format. Other supported formats are Storable and YAML.

PHP

Serialization in PHP is straightforward. The built-in function serialize() handles it in a single statement. <lang php>$myObj = new Object(); $serializedObj = serialize($myObj);</lang> In order to un-serialize the object, use the unserialize() function. Note that the class of object must be defined in the script where un-serialization takes place, or the class' methods will be lost.

PicoLisp

The built-in function pr serializes any kind of data, and rd reads it back. This functionality is also used internally for database access and interprocess-communication. <lang PicoLisp>(class +Point)

1. x y

(dm T (X Y)

  (=: x (or X 0))
  (=: y (or Y 0)) )

(dm print> ()

  (prinl "Point " (: x) "," (: y)) )

(class +Circle +Point)

1. r

(dm T (X Y R)

  (super X Y)
  (=: r (or R 0)) )

(dm print> ()

  (prinl "Circle " (: x) "," (: y) "," (: r)) )

(setq

  P (new '(+Point) 3 4)
  C (new '(+Circle) 10 10 5) )

(print> P) (print> C)

(out "objects.dat"

  (pr (val P) (getl P))
  (pr (val C) (getl C)) )</lang>

<lang PicoLisp>(in "objects.dat"

  (putl (setq A (box (rd))) (rd))
  (putl (setq B (box (rd))) (rd)) )

(print> A) (print> B)</lang> Output:

Point 3,4
Circle 10,10,5
Point 3,4
Circle 10,10,5

Python

<lang python># Object Serialization in Python

1. serialization in python is accomplished via the Pickle module.
2. Alternatively, one can use the cPickle module if speed is the key,
3. everything else in this example remains the same.

import pickle

class Entity: def __init__(self): self.name = "Entity" def printName(self): print self.name

class Person(Entity): #OldMan inherits from Entity def __init__(self): #override constructor self.name = "Cletus"

instance1 = Person() instance1.printName()

instance2 = Entity() instance2.printName()

target = file("objects.dat", "w") # open file

1. Serialize

pickle.dump((instance1, instance2), target) # serialize `instance1` and `instance2`to `target` target.close() # flush file stream print "Serialized..."

1. Unserialize

target = file("objects.dat") # load again i1, i2 = pickle.load(target) print "Unserialized..."

i1.printName() i2.printName()</lang>

Ruby

The core class Marshal handles object serialization. The dump method serializes an object, and the load method reconstitutes it. <lang ruby>class Being

 def initialize(specialty=nil)
   @specialty=specialty
 end
 def to_s
   "(object_id = #{object_id})\n"+"(#{self.class}):".ljust(12)+to_s4Being+(@specialty ? "\n"+" "*12+@specialty : "")
 end
 def to_s4Being
   "I am a collection of cooperative molecules with a talent for self-preservation."
 end

end

class Earthling < Being

 def to_s4Being
   "I originate from a blue planet.\n"+" "*12+to_s4Earthling
 end

end

class Mammal < Earthling

 def initialize(type)
   @type=type
 end
 def to_s4Earthling
   "I am champion in taking care of my offspring and eating everything I can find, except mammals of type #{@type}."
 end

end

class Fish < Earthling

 def initialize(iq)
   @iq=(iq>1 ? :instrustableValue : iq)
 end
 def to_s4Earthling
   "Although I think I can think, I can't resist biting in hooks."
 end

end

class Moonling < Being

 def to_s4Being
   "My name is Janneke Maan, and apparently some Earthlings will pay me a visit."
 end

end

diverseCollection=[] diverseCollection << (marsian=Being.new("I come from Mars and like playing hide and seek.")) diverseCollection << (me=Mammal.new(:human)) diverseCollection << (nemo=Fish.new(0.99)) diverseCollection << (jannakeMaan=Moonling.new)

puts "BEGIN ORIGINAL DIVERSE COLLECTION" diverseCollection.each do |being|

 puts "",being.to_s

end puts "END ORIGINAL DIVERSE COLLECTION" puts "\n"+"*"*50+"\n\n"

1. Marshal the diverse Array of beings

File.open('diverseCollection.bin','w') do |fo|

 fo << Marshal.dump(diverseCollection)

end

1. load the Array of diverse beings

sameDiverseCollection=Marshal.load(File.read('diverseCollection.bin'))

puts "BEGIN LOADED DIVERSE COLLECTION" puts(

    sameDiverseCollection.collect do |being|
      being.to_s
    end.join("\n\n")
    )

puts "END LOADED DIVERSE COLLECTION"</lang>

Tcl

Works with: Tcl version 8.6

This example uses an experimental package, available from The Tcler's Wiki. <lang tcl>package require Tcl 8.6 package require TclOO::serializer 0.1

1. These classes are inspired by the Perl example

oo::class create Greeting {

   superclass oo::serializable
   variable v
   constructor {} {
       set v "Hello world!"
   }
   method get {} {
       return $v
   }

} oo::class create SubGreeting {

   superclass Greeting oo::serializable
   variable v
   constructor {} {
       set v "Hello world from Junior!"
   }

} oo::class create GreetingsHolder {

   superclass oo::serializable
   variable o1 o2
   constructor {greeting1 greeting2} {
       set o1 $greeting1
       set o2 $greeting2
   }
   method printGreetings {} {
       puts [$o1 get]
       puts [$o2 get]
   }
   destructor {
       $o1 destroy
       $o2 destroy
   }

}

1. Make some objects and store them

GreetingsHolder create holder [Greeting new] [SubGreeting new] set f [open "objects.dat" w] puts $f [oo::serialize holder] close $f

1. Delete the objects

holder destroy

1. Recreate the objects from the file and show that they work

set f [open "objects.dat" r] set obj [oo::deserialize [read $f]] close $f $obj printGreetings</lang>