The Union Type Quiz

gistfile1.txt

Union type quiz
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Should there be predefined implicit widening conversions between numbers?

( ) Yes, even if they are lossy
( ) Yes, but only non-lossy ones
( ) No
( ) Other: ______________________________


What should be the inferred type of the expression
  List(1, 1.0)?

( ) List[Double]
( ) List[AnyVal]
( ) List[Int|Double]
( ) Other: ______________________________


What should be the inferred type of the expression
  List(1: java.lang.Integer, 1.0: java.lang.Double)?

( ) List[Number with Comparable[_ >: Double with Integer <: Number with Comparable[_ >: Double with Integer <: Number ...]]]
( ) List[java.lang.Integer|java.lang.Double]
( ) Other: ______________________________


Given the following declarations ...

  trait T
  object A extends T
  object B extends T

... what should be the inferred type of
  if (true) A else B

( ) T
( ) A|B
( ) Other: ______________________________


Does your answer change if
 - trait T is sealed?
   ( ) Yes, because: __________________________________________________
   ( ) No, because:  __________________________________________________
 - A and/or B are classes?
   ( ) Yes, because: __________________________________________________
   ( ) No, because:  __________________________________________________
 - A/B/T are type constructors?
   ( ) Yes, because: __________________________________________________
   ( ) No, because:  __________________________________________________


What should be the inferred type of
  if (true) Some(1) else None?

( ) Option[Int]
( ) Some[Int]|None
( ) Other: ______________________________


What should be the inferred type of
  if (true) Nil else List(1).asInstanceOf[::[Int]]?

( ) List[Int]
( ) Nil|::[Int]
( ) Other: ______________________________


When, if ever, should a nominal type be prefered to a more precise union type?

( ) Always
( ) Never
( ) Only if the element types enumerate all subclasses/subobjects of a sealed supertype
( ) Other: ______________________________


When, if ever, should a more precise structural type be prefered to a union type?

( ) Always
( ) Never
( ) Only if the structural type is specified explicitly
( ) Other: ______________________________


Given the following declarations ...

  trait T { def foo: Int }
  class A extends T { def foo: Int = ???; def bar: Int = ??? }
  class B extends T { def foo: Int = ???; def bar: Int = ???; def bippy: Int = ??? }

... which members are allowed to be called on an instance aOrB of type A|B?

[ ] aOrB.toString
[ ] aOrB.foo
[ ] aOrB.bar
[ ] aOrB.bippy


Will your choice from above break existing, valid code?

( ) Yes
( ) Yes, but it doesn't matter because: ______________________________
( ) No, because: ______________________________
( ) Maybe?


How will inference interact with structural types?
__________________________________________________
__________________________________________________


Please give your typing approach an intuitive name:
__________________________________________________


Please describe the guiding principle of your typing approach in one sentence:
________________________________________________________________________________
________________________________________________________________________________