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In this video, I'd like to
explain a little bit

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Pharo's different packaging
ways, in order for

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not to get lost in the future.

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When you install Pharo, you will
normally click on a link

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given, but if you go on
Pharo,

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the release at the moment
of this video

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is version 4, but version 5 will
be exactly the same.

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When I downloaded Mac OSX version,
I get this zip.

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If I unzip this zip,
I get what I call Pharo4 app.

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When I launch
Pharo 4 app, I get Pharo.

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Let's imagine we write

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"Hello". When I save,
it will save the environment.

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I click on Save.

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If I click on Quit now,
I will launch it again,

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and I will have exactly
"Hello", because saving the Pharo

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image is making a memory copy
with all the

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objects included Bytecode objects
and compiled methods.

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What is there in

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this application?

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On Mac, we can what is inside.

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If I click on Show Contents,
what will I see?

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I'm going ti find a Pharo virtual
machine and resources.

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And here, I will find a changes
file and an

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image file.

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The image file is the one that
really contains

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the objects representing the memory,
and the changes file

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is a file comprising all the
incremental changes

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done.
If I double-click

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on the image file,

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normally, depending on the
OS, I will launch it on

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a Pharo virtual machine that
I have installed, it

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will launch again my image file.

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This image file,
what happens with it?

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Let's imagine I define a classe.

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I'm going to define a package,

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"Add package" "ATest".

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In this package,

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I'm going to define
"MyStrangeClass".

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I define it and here, I put
"foooo" which returns

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42.

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If I save this image with
another name, I'm going

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to save it with the name

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Pharo40Stef.

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What did it do?

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I quit. It created another
pair

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image and change. In this changes
file, we won't open it

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because it is not readable
by a human, there is

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the methods code I have just
created.

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And if I launch again Pharo 4,
I'm gonna

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launch it using the virtual
machine, I get

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once more the snapshot, what
we call the system

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copy that I had done at a certain
moment

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before.

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Now, if I execute again
PharoStef image, what will it

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do?

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It will show me the system
with my new class.

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The Pharo 4 application,
it is what we call a Mac

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bundle which contains the Pharo
VM plus an image plus a change.

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If I double-click on it,
I don't have any choice, it

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will always choose Pharo image
because it is a script

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that has coded:
"Here it is, this is THAT image."

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In general, it is useful at
the beginning of the use of

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Pharo, but we do not use it.

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In general, either we use an
instruction of the command

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line which is something like

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Pharo-ui with
MyPharoImage.image

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and this will

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send the thing. Or if we use
command line and we

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don't want to have the ui, we
will do that kind of things.

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It means that Pharo is installed
somewhere in

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your system as a standard Unix
application.

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Now, you see on this page

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that you can download a
Pharo

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pair, you can
download a virtual machine.

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We are gonna download the
virtual machine and

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download an image pair
and also source.

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I'm gonna explain what it is,
this way we will have the

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3 at hand, we will play together.

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Now if I unzip the file
corresponding to

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Pharo Image and
Changes, I get this one.

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When I unzip, what do I get in
Pharo in this file?

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I get an image.

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We will do it in a mode where
you can

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see what is inside.

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It means that this file,
it is again an image pair

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corresponding to a certain
state of the snapshot or of the

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Pharo image, of the virtualised
system. Here, I can execute it

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on the Pharo image.

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I get a message,
what is this message?

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The system can work since
I can execute anything.

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I can run it.

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Now, I can do exactly what I
did before.

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I can define MyPackage,
and in MyPackage

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I will say MyStrangeClass.

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So we start to be used to it.

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I define a method:

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fooo 42. It asks for my
login.

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I can do as usual
"MyStrangeClass new foo"

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and I get 42.

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So, very good. I can save.

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I save it for example with
another name,

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Stef, I name it
PharoStrange.

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OK.

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What does it say?

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It says “I can’t find the source
file

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Pharo 4. 0." Why does it say this?

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When I open the browser, if I can
see for instance the

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AST code, this is not your code,
so we go at the top.

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The reason why the system

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doesn’t find the comments

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is that it is decompiling.

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So, we don’t see it because the methods
are

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too simple, but it decompiles
the code.

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Let’s go on something more
concrete.

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Here it decompiled the code,
the Bytecode represents an

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an argument and it knows very well
that this is an argument.

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But we lost the source.

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In general, the sytem source,
when Pharo

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is implemented, is stored in
a file called Pharo 4 source

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that you can find here.

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In general Pharo 4

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source will be installed once
on the system because

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this file is on read only,
and all your

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applications can use it.

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I have it here, I’m gonna unzipp it.

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Here I have Pharo4.source.

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If I quit without saving

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and I relaunch the application,
here anyway you see

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that it does exactly the same as
previously, it is to say

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that when I save a snapshot
giving it

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another name, I have once more
a system with 2 things:

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the image and its changes.

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Here if I take my old image,
there

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is no more error because
it has found the code and it

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knows that it corresponds to
the state there was

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when we launched the first image.

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Now if I use the second one,

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if I consider the file
AST-Core, first

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my classes have comments.

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Here these are really the names
people gave.

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If we look at this architecture,
what do we have?

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We have the source file
containing the system sources,

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in general, once the system is
compiled, the compiler

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doesn’t need the sources,

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the virtual machine and
image and change pairs.

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Image contains all the objects
that have been defined plus

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the system objects,
with the changes files which

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contains the deltas of what you’ve done
compared to the changes file.

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Each time you save you system,
it is

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as if you save a virtualised
image of your OS.

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This is exactly the same principle.

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If you look inside the Pharo 4
application,

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you will find those ressources.

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I have the Pharo 4 sources,
I have the image file,

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the changes file and somewhere
here the virtual

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machine with its plugins.