Tech Talk I gave at my company for the things I learned at Scala Days 2013

1. Scala Days 2013
by Hung Lin @hunglin

2. Scala the **** out of NYC
3 days event @ NYC
Scala Sunday @ meetup HQ: 8 talks
Shapeless workshop on Monday

3. Hot Topics
Scala 2.10
Style of Scala*
Asynchronous Programming - akka
Big Data / Streaming Data - Spark
Macro
Play

4. Keynote: Scala with Style
by Martin Odersky, creator of scala

5. What is OOP good for?
Fixed APIs with unknown implementations. e.g.
Simula67 for simulation, Smalltalk for GUI
Objects are characterized by state, identity and
behavior - Grady Booch

6. OOP v.s. FP

7. Guideline #1
Keep it simple
Simple Made Easy - Rich Hichey

8. Guideline #2
Don't pack too much in one
expression
find meaningful names for the intermediate results. It's
not easy but it's important

9. Guideline #3
Prefer Functional
vals v.s. vars
recursions or combinators v.s. loops
immutable v.s. mutable collections
transformations v.s. CRUD*

10. Guideline #4
But, don't diabolize local state
sometimes, mutable gives better performance
sometimes, mutable adds convenience

11. vars v.s. vals
var interfaces = parseClassHeader()...
if (isAnnotation) interfaces += ClassFileAnnotation
val parsedIfaces = parseClassHeader()...
val interfaces =
if (isAnnotation) parsedIfaces + ClassFileAnnotation
else parsedIfaces

12. loops v.s. combinators
val totalPrice = items.map(_.price).sum
val totalDiscount = items.map(_.discount).sum

13. val (totalPrice, totalDiscount) =
items.foldLeft((0.0, 0.0)) {
case ((tprice, tdiscount), item) => (tprice + item.price,
tdiscount + item.discount)
}
var totalPrice, totalDiscount = 0.0
for (item <- items) {
totalPrice += item.price
totalDiscount += item.discount
}

14. Guideline #5
Careful with mutable objects
val m = ArrayBuffer[Int]()

15. Guideline #6
Don't stop improving too early
shrink code by factor of 10 + make it more readable at
the same time
clean and elegant solutions don't come to mind at the
first time
it is fun to find better solutions

16. Choice #1
Infix v.s. "."

17. Choice #2
Alphabetic v.s. Symbolic
val xs = List("apples", "oranges", "pears")
xs.foldLeft("")((result, i) => result + i)
("" /: xs)((result, i) => result + i)

18. Choice #3
Loop, recursion or combinators
try conbinators first
if it becomes too tedious, or efficiency is a big concern,
try tail-recursion
use loop for simple case or for readability

19. Choice #4
Procedures or "="
DON'T use procedure syntax
def method: Unit = {
// operations
}

20. Choice #5
Private v.s. nested
use nested function to avoid passing parameters
use nested function for small functions
don't nest too many levels

21. Choice #6
pattern matching v.s. dynamic
dispatch
the expression problem, check out
, lecture 4.5 and 4.6scala class @ coursera

22. Choice #7
type parameters v.s. abstract type
members
try type parameters first
avoid Animals[_]
a good article by Bill Venners

23. Keynote: Scala in 2018
by Rod Johnson, creator of Spring

24. in 2018
Java is still alive
Enterprise apps are using Scala
Startups are still NOT using Scala

25. myths / points
Readability over cleverness, LOC, FP, ...
Scala needs coding standard
Scala needs to move slower
Embracing instead of hating Java

26. Any fool can write code that a computer can understand.
Good programmers write code that human can
understand.
- Martin Fowler

27. Debugging is twice as hard as writing the code in the first
place. Therefore, if you write the code as cleverly as
possible, you are, by definition, not smart enough to
debug it.
- Brian Kernighan

28. Asynchronous Programming

29. asynchronous v.s. parallel
what else?
who's doing it?

30. asynchronous v.s. batching

31. pitfall: thread pool?
for tomcat, one thread handles one request

32. pitfall: back pressure

33. pitfall: performance v.s. scaling issue

34. pitfall: theory v.s. reality
cost of thread context switch
# of threads v.s. # of CPUs
where is the bottleneck?

35. Some thoughts about our system

36. Upgrade to scala 2.10

37. Use akka
asynchronous programming
fault tolerance
modular design

38. Use case class for data model
treat data as map

39. Use finagle for service modules
play is not for REST API
why pay the cost of HTTP?
statistics
separate REST and Data layer
modularity

40. Questions?