Supported Option Type Syntactic Sugar

[sychoo]

Working on option type syntactic sugar. Referred to null safety in Kotlin.

• Supported T? as the sugar for option.Option[T].
• Supported a built-in None value that works for all T.
  • NONE = option.None[Dyn] <: option.None[T] for all T.
  • Note that NONE is equivalent to option.None[Dyn].

[JonathanAldrich]

Hi Simon, did you test this? Can you include a test case in the PR?

[sychoo]

Hi Simon, did you test this? Can you include a test case in the PR?

Hi Jonathan, I have tested the features I have implemented, and I have added a test case in the example folder. There are still several other features to be supported:

• The implicit conversion from T to T?.

  // this will convert "Hello" to option.Some[String]("Hello").
  val str: String? = "Hello"

• Support "!" operator that explicitly convert T? to T, raise an error if str is NONE.

  // this will convert type of str from "String?" to the type of str2 "String".
  val str2: String = str!

• Propagate None using ?. operator.

  type Nested
     val str: String?
  
  val n1: Nested? = new
     val str: String? = "Hello"
  
  // this will print "Hello" successfully.
  stdout.print(n1?.str.get())
  
  val n2: Nested? = NONE
  
  // this will print "NONE", since n2 is of NONE type, "?." operator is used to propagate NONE.
  stdout.print(n2?.str.get())
  
  val n3: Nested? = new
     val str: String? = NONE
  
  // this will print "NONE, since n3.str is of NONE type, "?." operator is used to propagate NONE.
  stdout.print(n3?.str.get())