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Complex Values
- 2. data workflows fragile systems complicated maintenance difficult ? something missing in conventional OO
- 3. Values - functional style makes a difference „ values | objects“ ! [MacLennan, 1982]
- 4. Value is abstract concept 42 abstraction no lifecycle stateless context-free
- 8. ComplexValue is immutable composite Text string: 'ComplexValue...' style: (Textstyle font: #{Helvetica} size: 60) top down tree
- 9. ComplexValues are real objects but without identity Value = behavior + content same class & content = same Value
- 10. ComplexValue is generated from a specification just one specification per Value AValue class>>localSpecification
- 11. Interface 42.13 200 true 'abc ' 16:30 1.9.2009 16:30 1.9.2009 #(13 ' xyz ' nil false 16:30) Struct{ id: ' djia.ind ' type: ' close ' date: ' 20090101 ' adj: ' yes ' sync: 0} Requestor Trade time: <Time> value: <Number> volume: <Integer> settled: <Boolean> Trade time: 16:30 value: 42.13 volume: 200 settled: true Request id: ' djia.ind ' date: 1.1.2009 type: #close adjusted: true
- 12. System Interface Files Graphics Database C calls Internet Inside Media
Editor's Notes
- <CH> introduces Thomas explains his role as layouter and text author introduces historic develoment of the idea <T> introduces Christian and his work met CH a year ago at ESUG Values are in all our work Recognizing them makes modeling easier improves readability Helps with maintenance
- <T> What we also found: Systems are fragile: different data workflows (Data not standardized. Sharing/aliasing between modules. Unexpected changes, Nil, errors, connection lost.) Complicated: variants not modeled, concurrency, understand legacy/foreign code, all-in-one solutions
- <T> what we also share is a functional style Makes a difference MacLennan said: distinguish Nature of data is often values. To ignore them leads to conceptional errors. Complementary concept handle them properly
- <T> MacLennan teaches us: Values are abstractions (universals, concepts) Values are never created or destroyed Values wont change Values are referentially transparent 2 Instances are not distinguishable So, you can share them Why not model that in software?
- <CH> Date Time Rectangle
- <CH> why is this a value? Output text should not change after creation literal representation really useful Concise and readable at a glance, easily understandable with all details and structure no magic practical, tool support, living code test code easy completer works fine
- <T>so, what is a ComplexValue? Values in Values create once – never change any content No cyclic structures Concrete, finite, complete
- <T> Can build class hierarchies same capabilities like a regular object
- <T> we want tool support ´for modeling specify attributes and generate Model exploration and model changing is easy
- <T> where we also can find values Configurations: move specifics from code into declarations excellent for the setup of modules and systems all benefits of normal source code
- <T> we dont know, why xml strings should live In an Image Not referencable
- <T>Adequate There are Values – why use Objects? Simple/Reliable Dont care No side effects, No cycles, No illegal Values <CH>Pretty Readable at a glance Concise and Understandable Practical Print and transportable Supported by tools (references, refactoring, formatter, highlighter) Trivial
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- Legal ways to create a value