Object serialization

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

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.

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.

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 #
 
#  Serialize #
put(target,(instance1, new line, instance2, new line));
printf(($"Serialized..."l$));

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

# Unserialize #
PERSON i1;
ENTITY i2;
get(target,(i1, new line, i2, new line));
printf(($"Unserialized..."l$));
 
printf((person repr, i1, $l$));
printf((entity repr, i2, $l$))

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. Sometimes a FORMAT can be manually created to handle these lengths and tags. Also note that ALGOL 68 is strongly types and the type (mode) of the objectis note stored, but compiled into the code itself.

Output:

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

E

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

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 }
    }
}

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

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

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.)

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()))

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) init; - (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) init {

 self = [super init];
 animalName = nil;
 numberOfLegs = 0;
 return self;

} - (id) initWithName: (NSString*)name andLegs: (NSInteger)legs {

 self = [super init];
 animalName = [name retain];
 numberOfLegs = legs;
 return self;

} - (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 {

 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) init; - (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 {

 self = [super init];
 hasFur = NO;
 eatenList = [[NSMutableArray alloc] initWithCapacity: 10];
 return self;

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

 self = [super initWithName: name andLegs: 4];
 hasFur = fur;
 eatenList = [[NSMutableArray alloc] initWithCapacity: 10];
 return self;

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

 [thing retain];
 [eatenList addObject: thing];

} - (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 {

 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 data];
 NSKeyedArchiver *arch = [[NSKeyedArchiver alloc]

initForWritingWithMutableData: data];

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

 // 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];

 // 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>

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>

Perl

Library: Storable

<lang perl>{

   package Greeting;
   sub new {
       my $v = 'Hello world!'; 
       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!'; 
       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>

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.

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

<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

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>