This programming environment allows up-to date access to an objects instance variables,
to a classes definition,
the set of messages which are implemented there (i.e. the protocol),
the source code of those methods, the execution state and much more.
In addition, cross references can be searched
(who sends which message, who implements which message, who references a variable etc.),
breakpoints can be set and modifications can be made to a class.
Modifications to a class can be made at any time - even while there are active instances of it around;
any modification is immediately effective (that does make a difference in programmers productivity !).
From the Smalltalk perspective, these systems are not "integrated" at all.
WorkspaceApplication open
and create a variable named "myPen" by selecting its "Add Workspace Variable"
menu item:
| view |
view := View new.
view width: 200.
view height: 200.
view open.
myPen := Pen in: view.
This creates and opens up another view.
In addition, it also creates a pen-instance and makes the workspace variable "myPen" refer to it.
Pens understands a bunch of messages, among them are:
To make the pen draw a rectangle, evaluate:
- go: distance
- makes the pen move forward the given number of pixels
- turn: degrees
- makes the pen turn clockwise the given number of degrees
myPen go: 50.
myPen turn: 90.
myPen go: 100.
myPen turn: 90.
myPen go: 50.
myPen turn: 90.
myPen go: 100.
myPen turn: 90.
To inspect the internals of an object, we use a so called Inspector,
which can be opened by sending the object to be inspect an "inspect"-message.
Try:
You will see (scroll down the left list if required)
that - among other - the pen keeps information about its current position
("locationX" and "locationY") and its drawing direction ("direction").
For now, ignore the other values you will see in the inspector.
myPen inspect.
Clicking on such an instance variable in the inspector will display its value in the right part of the inspectors window.
It is also possible to interactively send messages to the inspected object
from within the inspector,
by entering the message expression into the inspectors (right) code pane,
and evaluating it (using "doIt") just like in a workspace.
Within the inspector, the inspected object can be referred to by the name "self";
therefore, we can send messages to the inspected object,
even if no global- or workspace-variable refers to it.
As an excercise, let the pen draw something using self-messages from within an inspector.
Browsers are explained in detail in the "Programming Tools" sections of this online document - for now, lets just find the Pen-class (use the "Find-Class" menu function) and have a look at the Pen classes full protocol (select "*all*" in the protocol list, which is the second right list in the browsers upper area).
- - via the Launcher
- by pressing the browsers icon or selecting the "SystemBrowser" item in the classes menu.
- - via a Workspace
- by selecting an expressions text and then applying the "others"-"browseIt" popUp-menu function 1
- - via an Inspector
- the selector also provides a "browseIt" popUp-menu function for the selected private variable
Excercises:
Can you spot the "go:" and "turn" messages we used before ?
With the help of the browser, have a look into the implementation and see what is
going on there.
Find and try (in a workspace) the spiral and mandala messages.
Copyright © Claus Gittinger Development & Consulting
Copyright © eXept Software AG
<cg@exept.de>