Scala

Question 1

var x = 5

Answer 1

variable

Question 2

val x = 5

Answer 2

constant

Question 3

x = 5

Answer 3

constant, bad form!

Question 4

var x: Double = 5

Answer 4

explicit type

Question 5

def f(x: Int) = { x*x }

Answer 5

define function

Question 6

def f(x: Int) { x*x }

Answer 6

error: without “=” it’s a Unix-returning procedure

Question 7

def f(x: Any) = println(x)

Answer 7

Any is the root of the Scala class hierarchy. This function can take anything for parameter.

Question 8

def f(x) = println(x)

Answer 8

Syntax error: must have a type for every arg.

Question 9

type R = Double

Answer 9

type alias

Question 10

call by?
def f(x: R)

Answer 10

call-by-value

Question 11

call by?
def f(x: => R)

Answer 11

call-by-name (lazy parameters)

Question 12

(x:R) => x*x

Answer 12

anonymous function

Question 13

(1 to 5).map(*2)
or
(1 to 5).reduceLeft(+_)

Answer 13

anonymous function - underscore is positionally matched argument

Question 14

(1 to 5).map( x => x*x )

Answer 14

anonymous function: to use an argument twice, you have to name the variable

Question 15

(1 to 5).map(2)
or
(1 to 5).map(2)

Answer 15

anonymous function bound infix method. Use 2*_ instead.

Question 16

(1 to 5).map {val x=_*2; println(x); x}

Answer 16

anonymous function - block style returns last expression

Question 17

(1 to 5) filter {%2 == 2} map {*2}

Answer 17

anonymous function - pipeline style.

Question 18

def compose(g:R=>R, h:R=>R) = 
 (x:R) => g(h(x))
val f = compose({_*2),{_-1})

Answer 18

anonymous function - to pass in multiple blocks, need outer parenthesis

Question 19

val zscore =
(mean:R, sd:R) =>
(x:R) =>
(x-mean)/sd

Answer 19

currying

Question 20

def zscore(mean:R, sd:R) =
(x:R) =>
(x-mean)/sd

Answer 20

currying

Question 21

def zscore(mean:R, sd:R)(x:R)
   = (x-mean)/sd

Answer 21

currying (syntax sugar)

Question 22

val normer = zscore(7, 0.4)_

Answer 22

need trailing underscore to get the partial, only for the sugar version

Question 23

def mapmakeT(seq: List[T]) = seq.map(g)

Answer 23

generic type

Question 24

5.+(3); 5 + 3

1 to 5) map (_*2

Answer 24

infix sugar

Question 25

def sum(args: Int*) = args.reduceLeft(+)

Answer 25

varargs

Question 26

import scala.collection._

Answer 26

wildcard import

Question 27

import scala.collection.Vector

import scala.collection.{Vector,Sequence}

Answer 27

selective import

Question 28

import scala.collection.{Vector => Vec28}

Answer 28

renaming import

Question 29

(1,2,3)

Answer 29

tuple literal (Tuple3)

Question 30

var (x,y,z) = (1,2,3)

Answer 30

destructuring bind: tuple unpacking via pattern matching

Question 31

var xs = List(1,2,3)

Answer 31

list (immutable)

Question 32

var xs = List(1,2,3)
xs(2)

Answer 32

parenthesis indexing

Question 33

1 :: List(2,3)

Answer 33

cons

Question 34

Byte

Answer 34

8 bit signed value

Question 35

Short

Answer 35

16 bit signed value

Question 36

Int

Answer 36

32 bit signed value

Question 37

Long

Answer 37

64 bit signed value

Question 38

Float

Answer 38

32 bit floating point

Question 39

Double

Answer 39

64 bit floating point

Question 40

Unit

Answer 40

Corresponds to no value

Question 41

Null

Answer 41

null or empty reference

Question 42

Nothing

Answer 42

The subtype of every other type, includes no values

Question 43

Any

Answer 43

Supertype of any type. Any object is of type Any.

Question 44

AnyRef

Answer 44

The supertype of any reference type