Comparing Swift Programming Language for Generics Support

Apart from my daily job at Zalando iOS team, i stumbled across a problem which then lead to Generics programming. I was trying to wrap UITableViewDelegate into a protocol Extension inspired by the Protocol Oriented Programming. I soon stumbled across another piece of puzzle. Static Dispatch vs Dynamic Dispatch. This is a topic i will write extensively sometime later. Then I was scanning the internet and reading research papers. I was reading this Advanced Swift and inside it somwhere was a link to this research papaer titled “Comparision of Programming Languages on the basis of support for Generics (Gracia 2003)”. The paper was extended in 2007. The gist is, it compared various programming lanagueges like Java, C++ and Haskell among others. Then i asked can i extend this research paper to include Swift?

It turned out, i along with my collegues help wrote the paper which shall be public sometime soon. And i made a talk for these concepts and presented to the entire mobile team on iOS guild.

For more details, chekck out http://kandelvijaya.com/?p=422

Transcript

1. GENERICS “0 TO 0”
2. TEXT ▸ A Comparative Study of Language Support for Generic Programming (R Gracia 2003) ▸ An Extended Comparative Study of Language Support for Generic Programming (R Gracia 2007)
3. AGENDA ▸ Refine Queue ▸ Concepts/Protocols ▸ Common errors and why? ▸ Protocol Oriented Programming (IF⏲ ) ▸ Finale: Swift vs Haskell in Generics
4. INTRODUCTION GENERICS ▸ Grouping of similar functionality into a single Thing ▸ Parametric Polymorphism [not Just polymorphism] ▸ Compile Time / Static Polymorphism
5. QUEUE
6. TEXT QUEUE FOR INT
7. TEXT QUEUE FOR STRING
8. TEXT QUEUE FOR CGPOINT
9. TEXT 1000’S OF THESE ▸ Cant be extended
10. TEXT WHAT IS CHANGING
11. TEXT IDEA 1
12. TEXT ANALYSE ▸ all value semantics conform to Any Protocol by default ▸ Is it Generic?
13. TEXT . ▸ NOT GENERIC ▸ Type Erasure Model ▸ Heterogeneous set capable ▸ Objectie-C NSArray is somehow similar to this
14. TEXT IDEA 2:
15. TEXT . ▸ Generic ▸ Type Safe ▸ Homogeneous set capable ▸ T==> type deduction from call site
16. TEXT
17. TEXT SO WHAT?? ▸ Reduces redundancy
18. TEXT SO WHAT?? ▸ Type Safety
19. TEXT 1-….
20. TEXT SO WHAT?? ▸ Capability can be extended beyond the authors intention ▸ Originates from Set theory. Highly useful for FPs.
21. TEXT SO WHAT FOR US???? ▸ Swift uses Generics all over the Standard Library ▸ Swift has a great support for Generics ▸ Generics are awesome when all the <> brackets and T: U: make sense
22. TEXT OOOH
23. TEXT ADD!!
24. TYPELESS GENERICS
25. TEXT PROPER TYPED GENERICS + is not defined on all types: unfortunately!!!
26. + CONCEPTS ▸ + means lhs and rhs can be added. It is a concept. ▸ In C++ are just documented. No language support. YUK
27. TEXT CONCEPT == PROTOCOL ▸ Protocol to our rescue.
28. TEXT SO…… ▸ Expressive ▸ No Lies to the compiler
29. TEXT FULL PICTURE
30. TEXT FULL PICTURE
31. TEXT FULL PICTURE
32. TEXT AT CALL SITE
33. TEXT HOW IT COMPILES? ▸ during compile time a concrete function is created in place of generic function. This is Separate Compilation. ▸ LLVM is smarter than this.
34. TEXT TYPES ▸ A grouping of data structure ▸ Int, String, NavigationBarAppereance, classes.
35. TEXT TYPES ▸ Protocols that are complete by themselves are proper types
36. TEXT WHAT ARE NOT TYPES? ▸ Items that can not completely defined in isolation ▸ Don’t know what is the type of Self until conformed by some concrete Type
37. TEXT WHAT ARE NOT TYPES? ▸ Items that can not completely defined in isolation ▸ Element is unknown unless conformed by somebody
38. TEXT SO.. ▸ They are Generic placeholders (Incomplete Types) ▸ so is Array, ▸ But not Array<Int>. Its a complete Type.
39. TEXT THUS ▸ Protocols with Self requirement or associatedType requirement are not complete by themselves ▸ Thus, they cant be used like a Type ▸ They can be used to constrain other Types ▸ Examples: ▸ Queue<T> ▸ Array<T>
40. TEXT 2. TYPE CONSTRAINTS Reduce function over a Collection Type only when the elements are SignedInteger
41. TEXT NOTE: ▸ Make note that Swift provided “T:Comparable” which specifies T can be anything that conforms to a concept/ protocol Comparable. Whereas, T == Int would mean T must be a Integer type.
42. TEXT GENERICS VS LOOKS GENERICS
43. TEXT TYPE ERASURE MODEL ▸ Generic Placeholder gives Type safety and feedback on code analysis ▸ Concrete Type parameter casts the provided argument into the Type method accepts. Hence, losing Type information. Type Erasure Polymorphism model or Not So Swift Model
44. CODE
45. CODE
46. TEXT ARRAY OF PROTOCOL ▸ Array of Concrete Type cannot be implicitly converted to Array of Another Type ▸ But a single Concrete Type can be converted to
47. CODE
48. ▸ Protocol are a special construct which occupies 40 bytes ▸ Int are 8 bytes on 64 bit machine ▸ Array<Int> == Array<8byte contagious memory> ▸ Array<AType> == Array<40Byte contagious memory> ▸ Swift wont transform :=> performance, memory, type loss TEXT WHY?
49. TEXT MIXIN, DEFAULT IMPLEMENTATION ▸ DEMO ▸ Protocol Oriented Programming ▸ Avoid Subclassing ▸ Careful about: Static vs Dynamic Dispatch!!!!
50. TEXT
51. TEXT
52. TEXT
53. TEXT AT THE CALL SITE
54. TEXT AT CALL SITE
55. TEXT ANOTHER CLASS
56. TEXT WHAT WE GOT! ▸ Protocol Oriented Programming ▸ We can subclass only from 1 parent. This makes multiple inheritance easy without actually inheriting ▸ Retroactive modeling (WHAT)
57. TEXT RETROATTIVE MODELING ▸ Ability to add functionality after the Type has been defined completely. ▸ Even though Array is made by Swift Team we were able to extend it with useful function after 2 years finally.
58. TEXT GENERICS SUPPORT FOR SWIFT
59. TEXT Great Support For Generics
60. TEXT ANY QUESTION?
61. REFERENCES ▸ Programming". http://www.osl.iu.edu/publications/prints/2005/ garcia05:_extended_comparing05.pdf. N.p., 2016. Web. 22 May 2016. ▸ "Generics In Swift, Part 2 · Episteme And Techne". Austinzheng.com. N.p., 2015. Web. 23 May 2016. ▸ Cook, Nate. "Are Swift Generics Separately Compiled?". Stackoverflow.com. N.p., 2016. Web. 24 May 2016. ▸ "Mixin". Wikipedia. N.p., 2016. Web. 24 May 2016. ▸ Tsai, Michael. "Michael Tsai - Blog - How Swift Implements Generics". Mjtsai.com. N.p., 2016. Web. 24 May 2016.