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Discussion 4 - Tom Filip

History of Object Systems from Midterm Review - Sp2000.

- What is Sketchpad?
- What is Simula?
- What do they have to do with C++?

Sketchpad is an object-oriented drawing program. It was revolutionary in the way that it treated items on screen as objects, conserving the features, inheritance properties, for example. The slides mentioned that you could draw a house, and have a house object. This object could be duplicated, and if a chimney was added to one house, it would consequently appear on all other houses. This clearly relates to concurrent objects. If you make a person object, you can duplicate it any number of times, and if a name attribute is added to the person, all person objects will now have a name attribute.

Simula is a Finnish simulation language, which introduced the concept of private data / different processes per instance basis. Considering the person object, one person can be a "Pete", while another person can be a "Tom" - They both share the same features (have a name attribute), however, they are two differernt, independent instances. One object / process could not interfere with another's internals, unless requested / specified.

C++, being a OO-language, combines both these concepts. Objects can be created - support subclass / superclass structures - inheritance, "private" object data / resources, instantiation, static methods / objects, etc. Bottom line is that that's what Sketchpad and Simula led to - revolution in PC industry called object-oriented programming. Among other reasons, this way software is more scalable, portable, easily managable, responsibilities are distributed.

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