WEBVTT

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In this video, 
I’d like to show you

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how we can use the inspector
to navigate and

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understand the inside of 
the system.

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The inspector is like 
a microscope

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that will enable us to go
and explore the inside of

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of the system but also, as if
we could send probes 

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to modify the system.
It is as if we were

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a biologist which is in fact manipulating 
bacterias and making them react.

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So we are gonna have fun exploring
what are "Smalltalk globals".

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In fact, this is the name space,
it is to say, the place where

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all Pharo classes are stored.

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So it is a dictionary,
the system dictionary is

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a dictionary. What is interesting is
that, with the inspector,

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of I look the inspector, it is

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a big table with

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values inside.

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So for example, if I choose…
I don’t know… 

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Breakpoint, I see that in my 
table I have

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a key containing at least an object
that contains

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this object, that contains a
value key.

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What is interesting with the
inspector is that

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here, for instance, I see
that at element 2

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in the table, what do I have?

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I have what we call
a global variable.

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So a global variable, what
is it?

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It is an object composed of 
a key and a value.

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The key, if I click on it, I
see 

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that it is a ByteSymbol
representing the name, and if

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I go backward and I look at the

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value, here I will have a class.

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So we are going to go inside
the classes.

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Here I go back to the beginning.

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The new Pharo inspector, 

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named GT Inspector,
after the developers

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team who developed it for Pharo, 
will propose

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dedicated tabs.

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On the system dictionary,
what specific tabs 

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do I have? I have the tab
showing the pairs

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key/value for my classes,

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or I will only get the keys.

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The keys are a little less
interesting since I

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will only have the classes names

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in question.

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Something nice also is that
this  

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inspector, you see that I can
either browse, that means…

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let’s take an example…

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I have browsed, I go from an object
to another by

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selecting a path in the 
structure in question.

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If I consider the key for example,
if I consider

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the value, here I get the
class and if on this

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class, I go into its
methods dictionary…

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From the methods dictionary,
I could go on a

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compiled method etc.

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I really browse and with
this tool, I can

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limit the view of what I want 
to see or for example view all the flow.

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But what is nice, it is that
I can also add

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a new branch in my flow.

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That’s what we are going to do 
here. So let’s imagine that

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I minimize, I go back to the start.

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Here finally, let’s imagine
I say to myself: “I am

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interested by the point class.”

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I know that normally I can
access

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the point class by doing ”Smalltalk global"
at #Point.

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So here, I do it and I tell it

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execute it and open an

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inspector in the actual inspector.

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And here, all of a sudden,
if we look at

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the navigation, I made
a branching

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between the navigation I had and
the one I want to go to.

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So this is nice, it means that
you can type

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lots of expressions
and begin to the navigation.

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So here, what do we see?

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We see the point class as an object.

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In fact, the inspector shows us

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that there are tabs specific 
to classes.

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So here, the “Raw” tab shows

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us that the Point class is defined
in the

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Kernel category, it has an 
environment, it points on

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the same space, this is the 
encoding format of its

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instances, it has a layout.

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In short, this is the Pharo
implementation of what a class is.

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Now, what is really nice with 
this inspector, it is 

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that I can see, for example here
the definition,

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the comments and there are other
tabs such as all the references.

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So if I click on the reference,
here I will see

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that Point is really used

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in the @ method.

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I take a look once more,
this is the raw

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version of the information
which is an object representing

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a method and here its Source,
so each time I can

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choose which is the best

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representation for the task
I am doing.

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So let's go backward.

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If I look at

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my class, here I would like 
to go into the methods dictionary.

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What is the methods dictionary?

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It is a dictionary with a key
which is the name of the

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method and a value which is 
a compiled method, 

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an instance of CompileMethod.
So if I looked at the raw

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aspect, you see that it is
a little more annoying

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because I would have to
understand how are

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implemented the methods dictionaries
in order to

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interact with them, whereas here
it is not what I'm interested in,

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I want to look at a compiled method.

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So to see a compiled method,

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I choose degrees for instance, 
and I

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browse and all of a sudden
I get a CompileMethod.

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A CompileMethod is an object
which, once again, 

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proposes different ways to be
displayed by the inspector.

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Here you see a compiled method,

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in fact this is a data framework,
a table

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a little bit specific, it contains
Bytecode, 

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and literals. What are the 
literals?

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In the code, each time 
you have

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asFloat, arcTan,
degrees or RadianToDegrees,

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it needs to be stored somewhere.

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It is stored here, you see,
at the beginning

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of the compiled method.

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What does the Bytecode do?

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It refers to those objects

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in order to put them in the stack
and invoke the methods.

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So here, this is what we can 
see for example, if we look at

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the view, I minimize this,
if we look at the Bytecode

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view, what does it do?

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It does PushRcvr, so it puts 0
on the stack and do equal.

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What does it correspond to?

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If we look a little bit closely,

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I display it twice, 
this display mode is

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really very useful,
look at what we can do:

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if now I want to see

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the source, I choose
Bytecode there and

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and source here, those expressions 
correspond with each other,

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look it is displayed.

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So this is great.

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It means I can make a push of
the receiver instance 

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variable 0, I put 0 on the stack

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and I send the equal message.

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And here, it is great because it 
means

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that the person who is making
the 

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compiler can see that the Bytecode
he produced

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corresponds to the code structure.

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In the same way, he can easily

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see that...
I go backward...

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If I am at the top and I click
on Self,

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here I get my 2 compiled 
methods.

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I get my 2 compiled methods
and in fact

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I'd like to see 
if I have

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an abstract syntax tree,
an increase of abstract

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syntax and the source.
I can also browse inside.

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Here for example, in my tree
which can be 

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complicated for this method,
if I open all, I can see

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that if I select the temporary

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variable Time, I select

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the bite of code to which
it refers.

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This is great too.
Once more if

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I look at this... The message
that sends equal to X

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with 0 as an argument, this is 
this little part of the tree

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corresponding to this part here.

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The inspector enables me to 
manage, in the 

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tree textual representation
for example,

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the selections I have of the tree
nodes.

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This constitute a great tool
for example to help 

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people who develop Pharo compiler.

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You can find this approach
for

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each domain, so even for your
domain objects 

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you can extend the inspector,

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in order to propose facets and
views which make sense.