Container type

Data type like List[A], Option[A], Either[A, B] etc, can be viewed as a container of basic type, which means it can store one or many value along with some effect. TODO: explain what's effect. The A , B in square brackets is generic type identifier. We will explain more about generic type later. A another confusive name for container type is called [Higher Kinded Type](https://en.m.wikipedia.org/wiki/Kind_(type_theory)). For a long time, you don't need to care about that name.

Option

Option is used to replace the null in OOPL (Object Oriented Programming Language). If there is scenario that the function can not return a valid data, then you should probably use Option.

Here we have defined a function called divide, if the divident is 0, then the underlying divide operation / will throw a exception called ArithmeticException. Option is perfect to be used under this scenario. With None represents the error scenario, and Some wrap the actual value.

Both None and Some(value) are just the data type that extends Option.

def divide(m: Int, n: Int): Option[Int] =
  if (n == 0) None
  else Some(m / n)

Scala standanrd library has provided a lot of functions to make Dev's life much easier when dealing with Option. I strongly suggest you do following exercises in amm REPL.

Option.empty == None // true

Option(10) == Some(10) // true

Some(10).get // 10

None.get // NoSuchElementException

None.getOrElse(0) // 0

Some(10).fold(0)(_ + 2) // 12

None.fold(0)((x: Int) => x + 2) // 0

Either

Try

Tuple

List

scala> List(1,2,3)
res0: List[Int] = List(1, 2, 3)

scala> 1 :: 2 :: 3 :: Nil
res1: List[Int] = List(1, 2, 3)

Set

scala> Set(1, 1, 2)
res2: scala.collection.immutable.Set[Int] = Set(1, 2)

Seq

scala> Seq(1,1,2)
res3: Seq[Int] = List(1, 1, 2)

Map

scala> Map('a'->1, 'b'->2)
res4: res1: scala.collection.immutable.Map[Char,Int] = Map(a -> 1, b -> 2)

Stream:

TODO