ST xxx Dynamic ObjectOriented Programming with Smalltalk 1

ST — xxx Dynamic Object-Oriented Programming with Smalltalk 1. Introduction Prof. O. Nierstrasz © Oscar Nierstrasz

ST — xxx What you should know! How does Smalltalk differ from Java or C++? Where are Smalltalk programs stored? Where are objects stored? What was the Dynabook? Is a class an object? What is dynamic binding? What is the difference between a message and a method? © Oscar Nierstrasz 2

ST — xxx Can you answer these questions? What ideas did Smalltalk take from Simula? From Lisp? Is there anything in Smalltalk which is not an object? What exactly is stored in the changes file? If objects have private state, then how can an Inspector get at that state? How do you create a new class? What is the root of the class hierarchy? If a class is an object, then what is its class? The class of its class? … If you don’t know, how would you find out? © Oscar Nierstrasz 3

ST — xxx 2. Smalltalk Basics © Oscar Nierstrasz

ST — xxx What you should know! How can you indicate that a method is “private”? What is the difference between a comment and a string? Why does 1+2*3 = 9? What is a cascade? How is a block like a lambda expression? How do you create a new class? How do you inspect an object? © Oscar Nierstrasz 5

ST — xxx Can you answer these questions? Why does Smalltalk support single (and not multiple) inheritance? Is the cascade strictly necessary? Why do you need to declare local variables if there are no static types? How can you discover the class of GUI object? How does SUnit differ from JUnit? © Oscar Nierstrasz 6

ST — xxx 3. Standard Classes © Oscar Nierstrasz

ST — xxx What you should know! How are abstract classes defined in Smalltalk? What’s the difference between a String and a Symbol? Where are class names stored? What is the difference between self and super? Why do we need Blocks? How is a Block like a lambda? How would you implement Boolean>>and: ? What does inject: into: do? © Oscar Nierstrasz 8

ST — xxx Can you answer these questions? How are Numbers represented internally? Is it an error to instantiate an abstract class in Smalltalk? Why isn’t the assignment operator considered to be a message? What happens if you send the message #new to Boolean? To True or False? Is nil an object? If so, what is its class? Why does Arrayed. Collection>>add: send itself the message should. Not. Implement? © Oscar Nierstrasz 9

ST — xxx 4. Smalltalk Coding Idioms © Oscar Nierstrasz

ST — xxx What you should know! What does yourself return? Why is it needed? How is a new instance of a class initialized? When should you implement invariants and preconditions? What happens when we evaluate an expression with “print it”? Why should a method never send super a different message? How is super static and self dynamic? How do you make your code self-documenting? © Oscar Nierstrasz 11

ST — xxx Can you answer these questions? When should you override new? If instance variables are really private, why can we see them with an inspector? When does self = super? When does super = self? Which classes implement assert: ? What does self refer to in the method Snakes. And. Ladders class>>example? © Oscar Nierstrasz 12

ST — xxx 5. Seaside © Oscar Nierstrasz

ST — xxx 6. Debugging © Oscar Nierstrasz

ST — xxx What you should know! When should you explicitly return self? Why shouldn’t you redefine methods named basic*? Why are blocks not full closures? How do you provide access to instance variables that are collections, without breaking encapsulation? What is one of the most important uses of super? How does programming with Smalltalk differ from programming in a conventional static language? © Oscar Nierstrasz 15

ST — xxx Can you answer these questions? What will happen if you redefine the method class? When should you define accessors for instance variables? How can explicit references to class names make your application fragile? Where is the method halt defined? © Oscar Nierstrasz 16

ST — xxx 7. Best Practice Patterns © Oscar Nierstrasz

ST — xxx What you should know! How should you name instance variables? Why should you be suspicious of comments? How does Simple Delegation differ from Self Delegation? When would you use Double Dispatch? Why should you avoid introducing a Converter Method for an object supporting a different protocol? How do you sort a Collection? When should you use Lazy Initialization? © Oscar Nierstrasz 18

ST — xxx Can you answer these questions? Which patterns would you use to implement a transactional interface? How can Method Object help you to decompose long methods? Why is it a bad idea to query an object for its class? Why are you less likely to see Double Dispatch in a statically-typed language? How can you avoid Modifying Super? How can you avoid writing case statements? What pattern does Object>>-> illustrate? © Oscar Nierstrasz 19

ST — xxx 8. Refactoring and Design Patterns © Oscar Nierstrasz

ST — xxx What you should know! How does the Open-Closed Principle apply to OOP? What are signs that an object has clearly-defined responsibilities? How can you recognize misplaced methods? How should you refactor long methods? How can you eliminate duplicated code between unrelated classes? Why are type tests a code smell? When do design patterns themselves turn into code smells? Why is it a bad idea to use global variables to store Singleton instances? © Oscar Nierstrasz 21

ST — xxx Can you answer these questions? How do the Common Closure and Common Reuse Principles alter the usual notion of cohesion? How does refactoring differ from reengineering? Can refactoring be fully automated? In what situations does the Law of Demeter not apply? How do design patterns make use of delegation? Why are Long Parameter Lists a code smell? Are is. Nil tests a code smell? What design pattern could help you eliminate them? Is the Smalltalk System. Dictionary a good example of a Singleton? © Oscar Nierstrasz 22

ST — xxx 9. Understanding Classes and Metaclasses © Oscar Nierstrasz

ST — xxx What you should know! What does is-a mean? What is the difference between sending a message to an object and to its class? What are the responsibilities of a metaclass? What is the superclass of Object class? Where is new defined? What is the difference between class variables and class instance variables? © Oscar Nierstrasz 24

ST — xxx Can you answer these questions? Why are there no explicit metaclasses? When should you override new? Why don’t metaclasses inherit from Class? Are there any classes that don’t inherit from Object? Is Metaclass a Class? Why or why not? Where are the methods class and superclass defined? When should you define an indexed class? Are Java static variables just like class variables or class instance variables? Where is the System. Dictionary Smalltalk defined? © Oscar Nierstrasz 25

ST — xxx 10. Reflection © Oscar Nierstrasz

ST — xxx What you should know! What is the difference between introspection and intercession? What is the difference between structural and behavioural reflection? What is an object? What is a class? What is the difference between performing a message send and simply evaluating a method looked up in a Method. Dictionary? In what way does this. Context represent the run-time stack? What different techniques can you use to intercept and control message sends? © Oscar Nierstrasz 27

ST — xxx Can you answer these questions? What form of “reflection” is supported by Java? What can you do with a metacircular architecture? Why are Behaviour and Class different classes? What is the class Proto. Object good for? Why is it not possible to become: a Small. Integer? What happens to the stack returned by this. Context if you proceed from the self halt? What is the metaclass of an anonymous class? © Oscar Nierstrasz 28

ST — xxx 11. Working with Bytecode © Oscar Nierstrasz

ST — xxx What you should know! What are the problems of the old compiler? How is the new Squeak compiler organized? What does the Squeak semantic analyzer add to the parser-generated AST? What is the format of the intermediate representation? What kind of virtual machine does the Squeak bytecode address? How can you inspect the bytecode of a particular method? © Oscar Nierstrasz 30

ST — xxx Can you answer these questions? What different groups of bytecode are supported? Why is the Sma. CC grammar only BNF-“like”? How can you find out what all the bytecodes are? What is the purpose of IRBuilder? Why do we not generate bytecode directly? What is the responsibility of class Instruction. Stream? How would you implement a statement coverage analyzer? © Oscar Nierstrasz 31

ST — xxx 12. Traits and Classboxes © Oscar Nierstrasz

ST — xxx What you should know! Why does single inheritance lead to duplicated code? How does the composing class retain control of trait composition? What do “glue” methods do for traits? What is the “flattening property” and why is it important for traits? Why is there “inappropriate inheritance” in the Smalltalk Collections hierarchy? What is a “class extension”? In what way to classboxes ensure locality of changes? What problems are solved by combined traits and classboxes? © Oscar Nierstrasz 33

ST — xxx Can you answer these questions? Why do multiple inheritance and mixins leads to “fragile class hierarchies”? C++, Eiffel and Python all offer multiple inheritance – are they broken? Why don’t traits specify any state? How much code is duplicated in the standard Java libraries? What problems occur in Java due to the lack of class extensions? Can classboxes be “flattened” in the same way that traits can? Why or why not? © Oscar Nierstrasz 34

ST — xxx License > http: //creativecommons. org/licenses/by-sa/3. 0/ Attribution-Share. Alike 3. 0 Unported You are free: to Share — to copy, distribute and transmit the work to Remix — to adapt the work Under the following conditions: Attribution. You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license. For any reuse or distribution, you must make clear to others the license terms of this work. The best way to do this is with a link to this web page. Any of the above conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author's moral rights. © Oscar Nierstrasz 35