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![20 July 2017 Commutative Short Circuits 7Made available under EPL 1.0
2-valued truths, Inflated types
2-valued truths enforced by static analysis
no null values - safe navigation analysis
no invalid values - invalidity analysis
enforcement must be controlable
parsing / source text
e.g. Integer[1] - can only be an Integer
Integer[?] - may be null
new Integer[/] - may be null, may be invalid
model inflated types, N, N+1, N+2 values
Integer[1] conformsTo Integer[?] conformsTo Integer[/]](https://image.slidesharecdn.com/shortcircuits-170720180717/85/Commutative-Short-Circuit-Operators-7-320.jpg)
![20 July 2017 Commutative Short Circuits 8Made available under EPL 1.0
Summary
old: 4-valued commutative short circuits
inadvertent conflict between design decisions
new: distinct short circuit operators
2-valued Boolean truths
3/4-valued Booleans - legacy/bad code
behind the scenes: model inflated types
e.g. Boolean[1], Boolean[?], Boolean[/]](https://image.slidesharecdn.com/shortcircuits-170720180717/85/Commutative-Short-Circuit-Operators-8-320.jpg)
Uploaded byEdward Willink
Commutative Short Circuit Operators
This document discusses changes made to the semantics of short-circuit operators in OCL. Originally, short-circuit operators like "and" and "or" allowed for 4-valued logic and were commutative. However, this led to inconsistencies. The changes introduce distinct short-circuit operators that enforce 2-valued truths and are not commutative. Behind the scenes, types are modeled as inflated types to represent null and invalid values while maintaining compatibility with legacy code.
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Commutative Short Circuit Operators
- 1. Made available underEPL 1.0 Commutative Short Circuit Operators Edward D. Willink Willink Transformations Ltd Eclipse Foundation MMT Component co-Lead OCL Project Lead QVTd Project Lead QVTo Committer OMG (Model Driven Solutions) OCL 2.3, 2.4, 2.5 RTF Chair QVT 1.2, 1.3, 1.4 RTF Chair OCL 2017 @ STAF2017 20th July 2017
- 2. 20 July 2017Commutative Short Circuits 2Made available under EPL 1.0 Recreated OCL Design Decisions Truths - true, false commutative and/or : x and y = y and x Expressions should be modeled OCLExpression -> UML TypedElement => Types => BooleanType Functional => no Exceptions 'the' invalid value for bad returns Unspecified values / UML multiplicity 0 null value for undefined values => N+2 value inflated types, 4-valued logic Short circuits for awkward combinations x = null or x.doSomething()
- 3. 20 July 2017Commutative Short Circuits 3Made available under EPL 1.0 Commutative Short Circuits x = null or x.doSomething() short circuit: when x is null true or invalid => 4-valued logic commutative x.doSomething() or x = null commutative short circuit: when x is null invalid or true implementation must evaluate the invalid to index 4x4 Karnaugh map design intent implementation should not evaluate garbage
- 4. 20 July 2017Commutative Short Circuits 4Made available under EPL 1.0 Where did it go wrong? Truths - true, false commutative and/or : x and y = y and x Expressions should be modeled OCLExpression -> UML TypedElement => Types => BooleanType Functional => no Exceptions 'the' invalid value for bad returns Unspecified values / UML multiplicity 0 null value for undefined values => N+2 value inflated types, 4-valued truths/logic Short circuits for awkward combinations x = null or x.doSomething()
- 5. 20 July 2017Commutative Short Circuits 5Made available under EPL 1.0 Where did it go wrong? Truths - true, false commutative and/or : x and y = y and x Expressions should be modeled OCLExpression -> UML TypedElement => Types => BooleanType Functional => no Exceptions 'the' invalid value for bad returns Unspecified values / UML multiplicity 0 null value for undefined values => N+2 value inflated types, 4-valued truths/logic Short circuits for awkward combinations x = null or x.doSomething()
- 6. 20 July 2017Commutative Short Circuits 6Made available under EPL 1.0 2-valued truths, 4-valued logic old: short circuit and/or operators are Boolean old: Boolean and/or operators are commutative => short circuit operators are commutative new: short circuit operators are NOT commutative no-change: x implies y uses 4-valued logic change: x and y uses 2-valued truths new: x requires y uses 4-valued logic change: x or y uses 2-valued truths new: x obviates y uses 4-valued logic legacy compatability can offer 4-valued and/or
- 7. 20 July 2017Commutative Short Circuits 7Made available under EPL 1.0 2-valued truths, Inflated types 2-valued truths enforced by static analysis no null values - safe navigation analysis no invalid values - invalidity analysis enforcement must be controlable parsing / source text e.g. Integer[1] - can only be an Integer Integer[?] - may be null new Integer[/] - may be null, may be invalid model inflated types, N, N+1, N+2 values Integer[1] conformsTo Integer[?] conformsTo Integer[/]
- 8. 20 July 2017Commutative Short Circuits 8Made available under EPL 1.0 Summary old: 4-valued commutative short circuits inadvertent conflict between design decisions new: distinct short circuit operators 2-valued Boolean truths 3/4-valued Booleans - legacy/bad code behind the scenes: model inflated types e.g. Boolean[1], Boolean[?], Boolean[/]