Subtyping Covariance And Contravariance

1330 Views

Report

• #Subtyping Sample Code
  
  #type
  #Cat <: Animal (tuple isn't subclass of []int, but it's subtype)
  TypeCat    := tuple(int,int)
  TypeAnimal := []int
  
  #Function Type
  TypeA2A := type{_(:TypeAnimal) : TypeAnimal}
  TypeC2A := type{_(:TypeCat)    : TypeAnimal}
  
  #Like Functor
  FunctorA2A(X:TypeAnimal, Y:TypeA2A) : TypeAnimal = Y(X)  
  FunctorC2A(X:TypeCat,    Y:TypeC2A) : TypeAnimal = Y(X)  
  
  #Function
  FuncA2A(X:TypeAnimal): TypeAnimal := X
  FuncC2A(X:TypeCat   ): TypeAnimal := X
  #Instantiate TypeCat because X(TypeAnimal) cannot cast to TypeCat
  FuncA2C(X:TypeAnimal): TypeCat    := TypeCat(2, 3) 
  
  my_first_device := class(creative_device):
      OnBegin<override>()<suspends>:void=
          ValCat    :TypeCat    = (0, 1)
          ValAnimal :TypeAnimal = (100, 200, 300, 400)
  
          #covariance
          #(Animal->Cat) <: (Animal->Animal)
          Result1 := FunctorA2A(ValAnimal, FuncA2A)
          Result2 := FunctorA2A(ValAnimal, FuncA2C)