Transcript Where do objects come from? A brief history of object-oriented thought Dynabook to Personal Computer The Personal Computer* as we know it today was invented in.

Where do objects
come from?
A brief history of object-oriented
thought
Dynabook to Personal
Computer
The Personal Computer* as we know it today was
invented in pursuit of the Dynabook
(*And object-oriented programming, too!)
Start of the Story:
Late 60's and Early 70's
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Windows are made of glass, mice are undesirable rodents
Good programming = Structured programming

Verb-oriented
Structured Programming
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Define tasks to be performed
Break tasks into smaller and smaller pieces
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Until you reach an implementable size
Define the data structures to be manipulated
Design how functions interact
What's the input
 What's the output
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Group functions into components ("units" or "classes")
Write the code
Object-oriented programming
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First goal: Model the objects of the world
Noun-oriented
 Focus on the domain of the program
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Phases

Object-oriented analysis: Understand the domain
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Object-oriented design: Define an implementation

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Define an object-based model of it
Design the solution
Object-oriented programming: Build it
How’d we get from there to here?

How did we move from structured to
object-oriented?
 Key
ideas
 Master-drawings
in Sketchpad
 Simulation “objects” in Simula
 Alan
Kay and a desire to make software
better
 More
robust, more maintainable, more scalable
Birth of Objects, 1 of 2

Ivan Sutherland's Sketchpad, 1963
Sketchpad
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First object-oriented drawing program
Master and instance drawings
Draw a house
 Make two instances
 Add a chimney to the master
 Poof! The instances grow a chimney

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Other interesting features
1/3 Mile Square Canvas
 Invention of “rubber band” lines
 Simple animations

Birth of Objects, 2 of 2

Simula

Simulation programming language from Norway,
1966
Define an activity which can be instantiated as

Each process has it own data and behavior

processes


In real world, objects don't mess with each others'
internals directly
(Simulated) Multi-processing

No Universal Scheduler in the Real World
Alan Kay

U. Utah PhD student in 1966
 Read
Sketchpad, Ported Simula
Saw “objects” as the future of computer
science
 His dissertation: Flex, an object-oriented
personal computer

A
personal computer was a radical idea
then
Kay’s Insights
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“Computer” as collection of Networked Computers
All software is simulating the real world
Biology as model for objects
Bacterium has 120M of info, 1/500th of a Cell, and we
have 1013 of these in us
 What man-made things can scale like that?

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Stick a million dog houses together to get the Empire State
Building?
Internet does, but how can we make that the norm?
Birth of Objects

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Objects as models of real world entities
Objects as Cells

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Independent, indivisible, interacting -- in standard
ways
Scales well



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Complexity: Distributed responsibility
Robustness: Independent
Supporting growth: Same mechanism everywhere
Reuse: Provide services, just like in real world
Features of Objects
Encapsulation: Can't mess with the innards
 Aggregation: Objects can be created overand-over and combined within other objects
 Inheritance: Objects can get structure (data)
and behavior (methods) from another

Alan points out that Inheritance is not the
most important idea in objects.
 Empirically, more systems rely on
aggregation than inheritance.

"A Personal Computer for Children of All
Ages"

Flex, an object-oriented personal computer
Flex
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Enabled by Moore's Law
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Logo, Sketchpad, and Simula
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Imagining personal computing in 1969
Learning representations and knowledge through
programming them
Keyboard and drawing tablet
Computer as meta-medium

The first medium to encompass other media
Alan Kay’s Dynabook (1972)

Alan Kay sees the Computer as Man’s first metamedium
A medium that can represent any other media: Animation,
graphics, sound, photography, etc.
 Programming is yet another medium


The Dynabook is a (yet mythical) computer for creative metamedia
exploration and reading
Handheld, wireless network connection
 Writing (typing), drawing and painting, sound recording,
music composition and synthesis
 One goal: End-user programming.
 But WHY?

Prototype Dynabook
(Xerox PARC Learning Research Group)
A Dynabook is for Learning

The Dynabook offers a new way to learn new kinds of
things…and perhaps old things in better ways

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
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Dynamic systems (like evolution)
Especially decentralized ones (Resnick, 1992)
Knowledge representation (Papert, 1980)
Programming (Kay & Goldberg, 1977)
But need a system for creative expression

In a time when “windows” were made of glass, and
“mice” were undesirable rodents
Smalltalk-72

For the Dynabook,
WIMP was
invented:
overlapping
Windows
 Icons
 Menus
 mouse Pointer

How Smalltalk was Implemented
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Bytecode compiler

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Virtual machine to create the make-believe
computer

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Machine language for a make-believe computer
Invented years earlier by Burroughs
Used in UCSD Pascal, Java, Python, etc.
VM handles garbage collection, threading, etc.
Four files needed for this
implementation:
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VM (Very small: Typically less than 1M)
Image file (in bytecode)

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Almost all of Smalltalk is written in Smalltalk
Sources file (all sources always came along)
Changes file (added sources by user)

When you’re debugging how windows and addition works,
you will crash the system
1981: Xerox releases Smalltalk-80
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Smalltalk announced in August 1981 Byte magazine
To prove portability, sends tapes to IBM, Sun, Apple,
H-P, Tektronix
Smalltalk research starts up at all these places
 Some Tektronix oscilloscopes have Smalltalk inside of them

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Spins off ParcPlace to market Smalltalk
Adele Goldberg goes to run the new company
 Smalltalk-80 -> ObjectWorks -> VisualWorks
 ParcPlace -> ObjectShare + Neometron and then Cincom

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Other Smalltalks: Digitalk's Smalltalk/V and Quasar's SmalltalkAgents
Back to the Future:
Birth of Squeak
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1995: Alan Kay, Dan Ingalls, Ted Kaehler are all at Apple
Still want "A development environment in which to build
educational software that could be used—and even
programmed—by non-technical people and by children"
Build on Open Source Software strengths

Use the distributed power of Internet-based programmers
Squeak Team

Include John Maloney, Scott Wallace, and Kim Rose
Maloney from Self: O-O at nearly C speeds
 Wallace: End-user programming, programming
frameworks
 Rose: Education practice and study

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Wanted a new Smalltalk, but didn't have to build from
scratch
Apple had the original Smalltalk-80 still!
"Build everything in Smalltalk"
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"We
determined that implementation in C would be key
to portability but none of us wanted to write in C."
Make the Apple Smalltalk portable again
Write a new VM all in Smalltalk
Write a Smalltalk-to-C translator
Spit out the new VM on the new Smalltalk
Whole process: 16 weeks
Squeak
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Even from the beginning, powerful implementation

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Released to the net, and ported to Windows and UNIX within five
weeks

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Apple license allows commercial apps, but system fixes must be
posted
Squeak Team moves to Disney for several years.

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16 voice music synthesis, all in Smalltalk
In the end, it's about media.
Squeak today (over 30 platforms)
Media: 3-D graphics, MIDI, Flash, MPEG, sound recording
 Network: Web, POP/SMTP, zip compression/decompress
 Beyond Smalltalk-80: Exceptions, namespaces

Breaking the Lines
Six Basic Rules of Smalltalk
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Here’s the
part that
makes
Smalltalk
unusual
1. Everything is an object
2. All computation is triggered through message sends
3. Almost all of Smalltalk is <receiverObject> <message>
4. Messages trigger methods.
5. Every object is an instance of some class
6. All classes have a parent class, except for the root of the class hierarchy

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Parent is superclass, child is subclass
Subclasses inherit behavior and structure from parent class.
Sample Code
| anArray anIndex aValue | "Declare three local variables"
aValue := 2.
"Set aValue to 2"
anArray := Array new: 10. "anArray is an Array 10 elems"
1 to: 10 do:
"Store 2*index at each array elem"
[:index |
anArray at: index
put: (aValue * index)].
anIndex := 1.
"Walk the array again, printing out the values"
[anIndex <= anArray size] whileTrue:
[Transcript show:
'Value at: ',(anIndex printString),
' is ', (anArray at: anIndex) printString ; cr.
anIndex := anIndex + 1.]
Sample code output
Value at: 1 is 2
Value at: 2 is 4
Value at: 3 is 6
Value at: 4 is 8
Value at: 5 is 10
Value at: 6 is 12
Value at: 7 is 14
Value at: 8 is 16
Value at: 9 is 18
Value at: 10 is 20
Reviewing the Rules
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1. Everything is an object

aValue := 2
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Set the value of variable aValue to point to a SmallInteger object whose
value is 2.
aValue := 'fred'. Could follow immediately and would be perfectly fine
All variables can point to any object.
2. All computation is triggered through message sends

Even things like 1 to: 10 do: is just a message send
Reviewing the Rules
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3. <recieverObject> <message>
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1 to: 10 do: [] is a message
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1 is the reciever
to:do: is the message
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(Colons indicate an argument will follow)
10 and the block [] are the arguments
2 + 3 is a message

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2 is the receiver
+ is the message
3 is an argument
There are no predefined control
structures in
Smalltalk!
Reviewing the Rules
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4. Messages trigger methods

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to:do: whileTrue: and + are all messages that have corresponding methods
There can be more than one method implementing the same message
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Which method gets executed is based on the class of the receiver, and the decision is
made at runtime
This is late-binding
More than one kind of object can respond to the same message in its own way

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3 + 5 and 3.1 + 5.2 are very different methods
This is polymorphism
Polymorphism lets you program in terms of goals not code
Methods in class Object are accessible by every object by inheritance, like
printString.
Smalltalk isn’t the only language
like this

Self (from Sun) also has “pure” object-oriented semantics, like
Smalltalk.
Self is the fastest O-O language ever: 50% of the speed of C
 Incrementally optimizing compiler

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Used by Sun to create their Hotspot Java VM
Alan Kay on Java and C++
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“Java and C++ make you think that the new ideas
are like the old ones. Java is the most distressing
thing to hit computing since MS-DOS.”
"I invented the term Object-Oriented and I can
tell you I did not have C++ in mind."
Java and C++ keep the objects,
but lose the messages.

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Object.method() is a method invocation, but not a
message send.
The earliest Smalltalk’s were even allowed to change the
message->method binding

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Smalltalk-72 literally passed the entire sentence after the
receiver object to the receiver object.
The receiver object could parse the message any way it
wanted!
Problems:
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Different syntax for different objects -> hard to read.
Hard to make fast: Method lookup was slow.
Java/C++ go far the other direction: No late-binding of
message to method
The key to objects are messages
Just a gentle reminder that I took some pains at the last OOPSLA to try to remind everyone
that Smalltalk is not only NOT its syntax or the class library, it is not even about classes.
I'm sorry that I long ago coined the term "objects" for this topic because it gets many
people to focus on the lesser idea.
The big idea is "messaging" -- that is what the kernel of Smalltalk/Squeak is all about (and
it's something that was never quite completed in our Xerox PARC phase). The Japanese
have a small word -- ma -- for "that which is in between" -- perhaps the nearest English
equivalent is "interstitial". The key in making great and growable systems is much more
to design how its modules communicate rather than what their internal properties and
behaviors should be. Think of the internet -- to live, it (a) has to allow many different
kinds of ideas and realizations that are beyond any single standard and (b) to allow
varying degrees of safe interoperability between these ideas.
If you focus on just messaging -- and realize that a good metasystem can late bind the
various 2nd level architectures used in objects -- then much of the language-, UI-, and
OS based discussions on this thread are really quite moot. At PARC we changed
Smalltalk constantly, treating it always as a work in progress -- when ST hit the larger
world, it was pretty much taken as "something just to be learned", as though it were
Pascal or Algol. Smalltalk-80 never really was mutated into the next better versions of
OOP. Given the current low state of programming in general, I think this is a real
mistake.