Making Smalltalk: Spreading the OO Fun LG #59

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"Linux Gazette...making Linux just a little more fun!"

Spreading the OO Fun (Series Introduction)

By Jason Steffler

Abstract

    When I wrote the first Making Smalltalk with the Penguin article back in March of 2000 [LL], my target audience was experienced programmers who didn't have much exposure to OO programming or to Smalltalk. The article's intent was to give an overview of my favourite programming language on my favourite operating system. Since then, I've had a fair amount of email asking introductory type questions about Smalltalk and OO programming. So I thought I'd try my hand at a small series. It's been a while coming as after the first article I relocated from KS->CT and had a baby (obviously using the corporate 'I' here! :-)
    The target audience for this series are people new to OO or new to programming altogether. The intent is to not only introduce OO programming, but to also spread the fun of Smalltalking. Why do this format/effort when there's lots of good tutorials out there? Two reasons really: 1) Tutorials are great, but can be static and dated pretty quickly. 2) An ongoing series tends to be more engaging and digestible.
    To help address the second reason above, my intent is to keep the articles concise so they can be digested in under an hour¹. Hopefully, as newbies follow along, they can refer back to the original article and make more sense of it. I plan on having a touch of advanced stuff once in a while to add flavour and as before, the articles are going to be written for read-along or code-along people.
    Something new I'm going to try is to make the ongoing series viewable in a contiguous fashion and downloadable in one chunk for people who want to browse the series locally. To do this, click on TOC grapic to right. The articles are going to have 2 sets of links: one set for www links, another set for local links, indicated as: [LL]
    If you like what you're reading, drop me a line letting me know, and I'll keep putting precious time into it.

Why Smalltalk?

Before we can get into OO stuff, I feel the need to set the context of the articles. Unfortunately, this will take up the bulk of this first article, but it's an important thing to do. We'll finish with a little bit of OO stuff at the end, and get into it more in the next article.
I believe Smalltalk is the best environment to learn OO programming in because:

Smalltalk has a very active and very helpful community; when you post a question to the Smalltalk newsgroups you very often get an answer, unlike many other newsgroups
is very easy to learn... one of it's original design intententions was to be a learning environment for children
is a pure OO environment and encourages OO programming (as opposed to encouraging procedural/Object mixed programming)
cutting your teeth in Smalltalk makes you a better OO programmer in any other language, because of the previous bullet
is a portable environment: write once, run anywhere, so people can learn on whatever OS they're running (as opposed to just the M$ variety)
can look at and manipulate objects in real time; I haven't seen this ability in any other environment
Smalltalk is written in Smalltalk. You can view how the language is put together to learn the language, and you can change anything that you don't like about it.
has garbage collection, no manual memory management, no explicit pointers
is a literate language; by this I mean the syntax is very simple and is geared towards programmer readability.
there's lots of Cool Things that you can do in it that I haven't seen anywhere else (will have some examples along the way)
...and best of all: it's fun.

In particular, I'm going to use Squeak as the playing vehicle. You'll notice this is a different flavour of Smalltalk than I used in my first article. I've never used Squeak before, so this'll be a learning experience for me too. The reasons for this are:

It's a completely opensource project
It has some Really Cool features that I haven't seen in other flavours of Smalltalk
It has a comparitively small footprint and it's very easy to install
It has a strong Swiki site (a Wiki site hosted in Squeak, hence Squeak Wiki)

Quote of the day

In essence, Smalltalk is a programming language focused on human beings rather than the computer.
-Alan Knight

Installation stuff

Note: before you fire up Squeak, I need to warn you to not be put off by the sparten GUI. There's actually two types of GUIs in Squeak: MVC & Morphic, both of which have skins to implement specific look-n-feels. For at least the beginning of the series, I plan on sticking to Morphic without skins, as it's the newer GUI and I want to keep things simple.
To install Squeak, you basically need to download and unzip 4 files. RPMs are available for people who prefer them. For instructions on downloading and installing Squeak, see these installation instructions, or these installation instructions. (Note: I'm using v2.7 of Squeak, which isn't the latest version, but for the purposes of these articles, the latest-n-greatest version is not required unless otherwise noted)

First Looks

    Note: do not save anything until we get to that point below. The initial orientation and setup of squeak is a little painful, but by the time we're done here it'll be much more friendly.
    Now that you have Squeak installed, let's fire it up. Go to a command prompt, cd to the directory where squeak is, and type squeak Squeak-2.7.image. You'll see a window open, with 10 windows within it. Feel free to read the Welcome To... and Getting Started... windows. If you want to skip this and read them later, that's fine too. You'll notice that the look-n-feel is "weird", don't worry about this. There are reasons for this that I'll get to in a future article. You can also play around with the various Play With Mes (there's some neat things there). Feel free to mess around to your heart's content, try resizing things, moving them ,etc. Don't worry about breaking anything as we haven't saved anything yet. When you click on Play With Me 3, 6, 7 or 8, you need to click on the window to get into it. To get out of it, left click on the window background, and select previous project.
    When you're done playing, and you're back in the main view you started out in, middle click on the squeak background somewhere, and select quit, and no, as we don't want to save any changes. Now restart squeak, and move the Welcome To... window somewhere. Now middle click on the squeak background somwhere, and select save and quit. Now, restart sqeuak again... notice that the window is in the place where you left it. In fact, every time you save in sqeuak the state of the IDE is saved exactly as it was! ² All the window placements, all the code - everything is exactly where you left it. This is great for getting back up to speed quickly on what you were doing.
    For the read-along folks, here's what the Welcome To... & two of the Play With Me windows look like:

Now, let's do a little customization before we move on to examples. Open a workspace (middle click on the squeak background, select open...>workspace.) You'll notice that it's the same type of window as the Welcome To... and Getting Started... windows. Enter in the following code snippits:

    Preferences setPreference: #noviceMode toValue: true.
    Preferences setPreference: #inboardScrollbars toValue: true.
    Preferences setPreference: #useGlobalFlaps toValue: true.

Then highlight both lines and execute the code (middle click>do it). This is known as 'doing it' in Smalltalk. Congratulations, you just ran your first Smalltalk code. Don't worry about the symantics right now, just be aware that we set some preferences. Now, remember when I mentioned that we'd be using the morphic GUI type for these articles? To do this, middle click on the squeak background, select open...>morphic project. You'll see a small window appear called Unnamed1. Let's name this project something, as you've already probably experienced, clicking on the title of the window will bring up a rename prompt. Type in Making Smalltalk. If you want, you can resize the window to see the whole title.
Now, let's enter the project, do this by clicking on the project to give it focus, then clicking on it again. You'll notice there are four tabs arranged around the screen (Menus, Squeak, Tools, and Supplies). If you mouse over the tab, a pop up menu will appear with neat stuff on it. If you mouse over the Menu tab you'll see the open... menu in the top left corner, select workspace to open up a workspace. You'll notice the look-n-feel is a little different now, as we're using the Morphic type of GUI; this project will be the basis of these articles.

One thing you'll notice from the menus, is that there's no saving option. Since we want to save everything we've done, let's get that menu. To do this, right click on the project background, you should see a series of different coloured dots around the screen. We're not going to get into their purpose just yet. Now left click on the red dot in the top left hand corner of the screen, you'll see a playfield menu, select keep this menu up. Now the menu is sticky, and you can move it around. Let's move it out of the way of the flaps to the bottow left hand corner of the screen. Finally, let's save what we've done, on that menu you just made sticky, click on save. Your window should look something like:

Getting to objects

    As I mentioned, the bulk of this article is going to be setting the stage for future articles. Now we can finally start addressing the topic at hand. There are many different definitions of what an object is. One way of thinking about it is that an object is anything you can think of that is a noun. A window, a menu, an array, a GUI, a string, an integer, a person, a tree, etc. This is a very simple view of what an object is, and we'll refine the definition over time.
    In Smalltalk, everything is an object³.   Unlike other languages where small building blocks like integers or strings aren't objects, everything is an object. If you have procedural programming experience, this is a good mantra to repeat for about 6 months.
    Let's start with the venerable Hello World example, but with a minor update (sheesh, we're not back in the '60s here). Instead of printing a string to the stdout (to the command line), let's open a window with the string in it. In the workspace enter and 'do':

(Workspace new contents: 'Hello World') openLabel: 'Hello World Workspace'

You'll see:

Remember when I said everything is an object? Well, we asked a new Workspace object to make its contents Hello World, then asked it to open itself with the label 'Hello World Workspace'. Notice there's no 'main' method, no compiling and linking step, no switching between a text editor and a compiler. The simplicity of being able to just type Smalltalk code and run it is very refreshing.
...but this old example is pretty worn out. Let's do something a little more up to date⁴. Let's make a line; in the workspace enter and do:

    World addMorph:
        (PolygonMorph
         vertices: {50@50. 200@200}
         color: Color red
         borderWidth: 20
         borderColor: Color red)

You'll see:

Here, we asked the project (World) we're in (projects are objects too) to add a morph that is a red line from point 50x50 to point 200x200. Now, let's play with this object a little bit, if you right click on the line object, you'll get the various multi-coloured points again (these are called halos). If you mouse over the line object, you'll see pop-up help describing what the halos do (Rote, Change size, debug, Duplicate, Move, etc). Left click on the yellow halo, and resize the line a few times. Try the rotate, duplicate, move buttons to play some more. Finally left click on the 'X' button when you want to get rid of the line object(s).
To make this first article digestible, I'm going to stop off here. Before I go though, I'm going to introduce the 'Sweet Squeak' section...

A Sweet Squeak

This section won't explore/explain code or example, but merely present a neat thing to try out⁵. This time, lets view a shockwave file. If you have an internet connection up, try entering this code and do it: (note, might take a while over 28.8; I did this at a friend's place with a 128K ISDN and it was pretty snappy)

   (FlashMorphReader on: (HTTPSocket
        httpGet: 'http://www.audi.co.uk/flash/intro1.swf'
        accept:'application/x-shockwave-flash'))
    processFile startPlaying openInWorld.

Looking forward

The next article will discuss Objects again as well as classes, messages and encapsulation.
Also, if any Squeakers out there know of something neat that can be easily done, let me know and I'll add it if there's room.

Questions and Answers

As opposed to including already answered questions via email, I'm going to start this section with a clean slate to address questions (as I have time) that this series raises. If you want a faster response, try posting your question to the comp.lang.smalltalk newsgroup, or the Swiki.

Article Glossary

This is a glossary of terms that I've used for the first time in this series, or a term that I want to refine. If you don't see a term defined here, try the ongoing glossary [LL]

IDE
        Integrated Development Environment.   An environment that programmers use to develop code in that they can program and debug in.
[LL]
        relative Local Link, use this link when browsing these articles locally
Object
        (def 1-simple) An object is anything you can think of that is a noun. A window, a menu, an array, a GUI, a string, an integer, a person, a tree, etc.
OO
        Object Oriented Briefly, this is a popular style/methodology of programming that these articles are going to introduce.
Project
       A specific view of the code. You can have multiple simultaneous views of the code. This is very handy if you're doing two or three projects at once, and don't want to lose track of where you're are in them.
Wiki site
        A series of web sites where there is no designated editor (for the most part, the odd page may have a password). If you see a way to improve the site, you can do so yourself! If you don't understand something, just edit the web page and type in your question!

Footnotes

[1] Keeping the articles concise will actually be the biggest challange. There's such a wealth of information that it's hard to convey just what is needed. To that end, I plan on making some simplifications as I go along and gradually refine them to reflect the technicalities.
[2] This is a feature common to all Smalltalk flavours that I know of. It's one of the many thinks I like about Smalltalk.
[3] This is the same assertion that I made in the first article, and I had a pile of people email me about how this isn't technically accurate. I thought from the context of the article that it would be apparent that this was a simplified generalization, oh well. This time I'll be explicit: this assertion is technically not accurate: not everything in Smalltalk is an object, but the vast majority of things are. For the beginner, it's a helpful simplifying view to have. I plan on refining this view later on.
[4] This snippet is from a Swiki entry by Dan Ingalls
[5] This snippet is also from the Swiki