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The Undiscoverable/Squeak (view source)
Revision as of 18:15, 24 August 2012
, 18:15, 24 August 2012→Creating an Object: Smalltalk
Below those are a text pane for various purposes, with a row of buttons at the top These buttons open other windows for various purposes. At the bottom is a comment pane where the programmer can explain the purpose of the Object type being viewed and how it is to be used.
Below those are a text pane for various purposes, with a row of buttons at the top These buttons open other windows for various purposes. At the bottom is a comment pane where the programmer can explain the purpose of the Object type being viewed and how it is to be used.
==Smalltalk Language==
Smalltalk is an extremely powerful, expressive, modular language with a number of other virtues. All of a Smalltalk system is written in Smalltalk, including a compiler that turns Smalltalk program text into platform-independent bytecodes. At runtime, a Smalltalk image runs on top of a highly portable Virtual Machine that provides system facilities and the lowest-level object functions, including a bytecode interpreter that runs all of the higher-level code.
The VM also exists inside Smalltalk as a model written in a subset of Smalltalk, allowing Smalltalk to run on a modified VM inside the current Smalltalk in order to debug the new VM. A satisfactory new VM is then translated to a highly portable subet of C, which can be compiled for all supported platforms in short order. The new compiled VMs are then packaged with the new Smalltalk (or Squeak or Etoys) image, including the Smalltalk model of the new VM, for distribution.
Everything in Smalltalk is an object. All Smalltalk programming consists of defining object classes and sending messages to objects, where the messages can refer to other objects. Every object is a member of a class that defines its structure in terms of internal data objects and methods of interpreting messages sent to the object
Open the Tools palette and drag a new Workspace into the world. Type 3+4 in the window, and make sure to leave the cursor on that line. Middle-click and select print it from the menu.
[[File:SqueakWorkspaceMenu.png]]
Smalltalk evaluates the expression and displays the value in the Workspace, thus.
[[File:Squeak3+4PrintIt.png]]
The number 3 is an object, a member of a numeric class of small integers. We send it the message + 4, invoking the method for + on that kind of integer with the argument 4, referring to a different object. We get back the object 7, and the interpreter invokes a method for printing that result in our Workspace.
A brief introduction to the subset of Smalltalk used in these pages is on the [[The Undiscoverable/Smalltalk|Smalltalk]] page. There are several good textbooks on Smalltalk.
==Creating an Object==
==Creating an Object==