You probably have participated many times in those battles which language is better. Sometimes you definitely have been using "weak/strict typing" definition. I would like to talk about it. It is too important to ignore. I want to compare several different languages and show you how delusional those "weak/strong" definitions. We will meet some math along with Javascript, Java, Scala, C++, .Net, Haskel and several others on the way to the truth. We will spill some blood and may lose some comrades but as a reward survivors will touch the future (a bit) of nextgen languages (let's name it as features of Java 40.0).

1. Types:
Weak/Duck/Optional vs Strong/Strict
Let the War Begin!

2. Victor Polischuk
13 years of experience
Tech Leader
@alkovictor victor-cr
Infopulse
BICS

3. Types
Strong
Static
Manifest
Weak
Dynamic
Implicit

4. Static
Dynamic
Verification Phase

5. Java
C#
C
JavaScript
PHP
Groovy
Static
Dynamic

6. Implicit
Manifest
Type Inference

7. Haskell
Scheme
JavaScript
Java
Pascal
C
Implicit
Manifest

8. Strong
Weak
<TooManyDefinitionsException>

9. When you use “strong” in a sense of “static”
– you hurt a puppy

10. Strong
vs
Weak
Runtime type information
Restrict variable type
Type conversions

11. JavaScript
Java/Scala
C#
Type Strength/Weakness

12. JavaScript
Java/Scala
C#
Type Strength/Weakness

13. Type Safe
Well-typed program cannot “go
wrong”
•Arthur John Robin Gorell Milner

14. What Is “Type Safe”
Memory safe
Ensure proper semantic for operations

15. Formal Type System
•Context: {<v, T>,…,<v, T>}
•Operation: (T, …, T) -> T

16. Hey, you!! Tell them about lambda calculus!!!

18. Formalizing The Type System

19. Expression
𝑒 = 𝑥
𝑒 = 𝑒1(𝑒2)
𝑒 = 𝜆𝑥. 𝑒
𝑒 = 𝑙𝑒𝑡 𝑥 = 𝑒1 𝑖𝑛 𝑒2

20. Examples in Java
Variable: int x = y
Application: increment(x*y)
Abstraction: x -> x + 2
Substitution: ((Predicate) (x -> x == 0)).apply(y)

21. Types
mono 𝜏 = 𝛼
mono 𝜏 = 𝐷 𝜏1 … 𝜏 𝑛
poly 𝜎 = 𝜏
poly 𝜎 = ∀𝛼. 𝜎

22. Examples in Java
Monotypic:
String
Map<Integer, Object>
Polytypic:
T
Map<String, T>
Predicate<T>
Function<T, K>

23. Context
Γ = ϵ
Γ = Γ, 𝑥: 𝜎

24. Dude

25. Context
Γ = {𝑥1: 𝜎1, … , 𝑥 𝑛: 𝜎 𝑛}

26. Typing

27. Formalizing The Type System
Variable Access:
𝑥:𝜎∈Γ
Γ⊢𝑥:𝜎
Application:
Γ⊢𝑒0∶𝜏→𝜏′ Γ⊢𝑒1:𝜏
Γ⊢𝑒0(𝑒1):𝜏′
Abstraction:
Γ, 𝑥:𝜏⊢𝑒:𝜏′
Γ⊢𝜆𝑥.𝑒:𝜏→𝜏′
Substitution:
Γ⊢𝑒0∶𝜎 Γ, 𝑥:𝜎⊢𝑒1:𝜏
Γ⊢𝑙𝑒𝑡 𝑥=𝑒0 𝑖𝑛 𝑒1∶𝜏

28. Free Type Variables
𝑓𝑟𝑒𝑒 𝛼 = 𝛼
𝑓𝑟𝑒𝑒 Γ =
𝑥:𝜎∈Γ
𝑓𝑟𝑒𝑒(𝜎)

29. Formalizing The Type System
Specialization:
Γ⊢𝑒:𝜎′ 𝜎′⊑𝜎
Γ⊢𝑒:𝜎
Generalization:
Γ⊢𝑒:𝜎 𝛼∉𝑓𝑟𝑒𝑒(Γ)
Γ⊢𝑒:∀𝛼.𝜎

31. Well Typed You Say?
There is a lot of math under the hood
Correctness can be proved
Tests are heuristics and have no future

32. Print All Permutations: JavaScript

33. Print All Permutations: Java

34. Print All Permutations: Java 8

35. Print All Permutations: JavaScript

36. Print All Permutations: Scala

37. Print All Permutations: Scala

38. Print All Permutations: C#

39. Print All Permutations: Haskell

40. So What Shall We Do?Learn
Math
Other Languages
Computer Science

41. Future
Project Valhalla
• Value types
• Improved generics
Correctness Proving
• Functions as first-class citizens
• Dependent types

42. Questions
Thank you for attention