Quick recap

Rony led a comprehensive discussion on the concept of data types, abstract data types, and their implementation in the Rex programming language, with a focus on object-oriented programming and multi-threading. He also demonstrated the creation of new instances, the use of directives, and the importance of understanding the terminology and scope of different variables. The team also addressed technical issues, the development of Rex, and the potential for future in-person meetings.

Next steps

Here are the key action items from the meeting:

All participants to create two short programs implementing concepts learned, working together in groups.

All participants to review the recording links that will be sent by Rony.

Priska to try the Alt + 126 keyboard shortcut to input the tilde character.

Peter to help tutor Kim and bring her up to speed if she missed content.

Peter to consider attending the Rex Symposium in May.

Rony to experiment with reducing screen resolution to 1024x768 for future recordings to reduce file sizes.

Rony to send recording links from today's session to participants.

Rony to inform the other absent participant that Peter offered tutoring assistance.

Summary

Understanding Data Types and Abstract Data Types

Rony led a discussion on the concept of data types, seeking informal definitions and associations from the group. The team struggled to provide a clear definition, but Prisca offered her interpretation, linking data types to the elementary school concepts of colors, sounds, and letters. Rony then elaborated on this, explaining that data types are used to express information through letters or characters, using the example of writing names or creating strings of characters. He further clarified the concept of abstract data types, which are general descriptions of data types, and encouraged the team to invent their own data types. Rony also discussed the implementation of data types in their system, emphasizing the importance of understanding the terminology and the use of methods to define the operations of an abstract datatype.

Understanding ADT and Object Messaging in Rexx

Rony explained the concept of Abstract Datatype (ADT) and how to create new instances using the 'new' message, using the string class as an example. He also discussed the alternative, simpler method for creating strings in All Rexx and the influence of the older programming language, Small Talk, on the development of All Rexx, particularly in the concept of interacting with objects through messages. Rony further clarified the process of object messaging in Rexx and introduced the concept of cascading messages. Reggie was present and asked questions to better understand the process. Rony also provided an example to illustrate the practical application of these principles.

Rony Demonstrates Abstract Data Type Implementation

Rony demonstrated the implementation of an abstract birthday data type and its usage, including the creation and assignment of values to different objects. He explained the concept of scope, its visibility rules, and the new Program Scope introduced by Regs, which makes all classes and routines defined via directives always visible and available for use throughout the program. Rony also clarified the differences between method and routine scopes in the Rex language, and introduced the concept of floating methods. Finally, he demonstrated the implementation of the abstract data type 'Person', showed how to use cascading messages to increase salaries, and suggested an alternative solution without cascading messages.

Class-Based Programming and Garbage Collection

Rony discussed the process of creating objects in a class-based programming language, emphasizing the importance of the 'Init' method for initializing object attributes. He also introduced the concept of garbage collection, explaining how it helps to manage memory by periodically identifying and destroying unused objects. Lastly, he highlighted the significance of the 'uninit' method in certain situations, such as when an object holds a system-wide lock, allowing it to release the lock before being destroyed.

Rex Development and Virtual Keyboard Issue

Rony took a short break before discussing an intriguing aspect related to classes. Reggie asked about the development of Rex, and Rony explained it was originally created in the Hursley lab by a team led by Shaw, with contributions from an English gentleman named Simon Nash and Rick McGill who later moved the development to the United States. Rony also addressed Prisca's issue with the virtual keyboard being in German and not allowing her to change the language. Rony suggested she try changing the language in the virtual machine settings, and they agreed to revisit the issue later.

Classification Tree and Object-Oriented Systems

Rony explained the concept of a classification tree in object-oriented systems, likening it to the biological classification of species. He emphasized the efficiency of the system, the possibility of multiple inheritance, and the importance of understanding the terminology in object-oriented systems. He also discussed the resolution of methods and the use of 'super' and 'self' variables, hinting at further exploration of these concepts in future discussions.

Inheritance, Class Definition, and Multithreading

Rony used the example of a special interest group for dogs to explain the concept of inheritance and class definition. He demonstrated how to implement different dog types, each with unique barking patterns, and emphasized the importance of understanding the differences between normal, little, and big dogs. Rony encouraged participants to come up with their own comparable data types and to use the subclass keyword to specialize existing classes. He also clarified the output of the program and introduced the topic of multithreading, promising to explain it in a future session.

Multi-Threading in Application Programming

Rony discussed the concept of multi-threading in application programming, highlighting its potential benefits and challenges. He explained that multi-threading allows different parts of a program to execute concurrently, but it can lead to issues such as data integrity problems and deadlocks. Rony emphasized that these issues can be addressed by using the intra-object and inter-object multi-threading capabilities provided by the Oorex programming language. He then invited questions and prepared to continue the presentation with a repetition of the most important concepts.

Rony's Rex Programming Language ADTs

Rony discussed the implementation of abstract data types (ADTs) using the Rex programming language. He explained the process of creating ADTs, emphasizing the uniqueness of each value and the importance of encapsulation. He demonstrated how objects communicate via messages and how to send messages to objects. Rony also discussed the use of directives in the setup phase of a program, the five different scopes defined in Object Rexx, and the process of object creation. Lastly, he introduced the concepts of object deletion, the classification tree, and method resolution in super classes, highlighting the role of special variables 'super' and 'self' in this context.

Dog Sanctuary Solution and Multi-Threading

Rony presented a solution to a problem involving a special interest group dog sanctuary, using inheritance to define different classes of dogs (normal, big, and little) and their respective barking behaviors. He also touched on the concept of multi-threading, emphasizing its potential benefits and pitfalls. A question was raised by Sharlet about the location of class links, which Rony clarified were sent via email. The conversation ended with Rony preparing to discuss the implementation of abstract data types using different directives.

Class Directive and Resource Directive Explained

Rony explained the various sub-keywords used in the Class Directive for defining abstract data types, including the concepts of subclass and metaclass. He demonstrated the use of multiple inheritance in a program involving three classes and clarified the historical and terminological reasons for using mix and class over subclass. Rony further explained the Method Directive, Attribute Directive, and Constant Directive, which are used to create getter and setter methods, instance methods, and class and instance methods that return a constant value, respectively. Lastly, he introduced the Resource Directive, which allows for the creation of resources, such as multi-line text, that can be accessed and output efficiently.

Short Programs, Attributes, and Methods

Rony emphasized the importance of creating short programs to better understand concepts and encouraged group sessions for learning and problem-solving. He clarified several technical aspects, including the concepts of attributes and methods in object-oriented programming, and their impact on multi-threaded programs and storage. The group also discussed the challenges faced by students, with Peter offering assistance to a struggling student and expressing his intention to attend a symposium in May. The possibility of a future in-person meeting was also discussed.

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