Classes in Luna can also take type parameters, making them polymorphic in some values. For an example, consider the previous definition of
class Vector: x y z :: Real
What if we needed a
Ints? In the current approach, it would require us to create another class just for this purpose. We can, however, add a type parameter to the
class Vector a: x y z :: a
Equipped with this definition, we can create vectors containing elements of any type, such as
Vector "hello" "world" "!" :: Vector Text Vector 1 2 3 :: Vector Int Vector 1.0 2.0 3.0 :: Vector Real
It is also possible to implement methods that assume some additional properties of the type
a (such as supporting arithmetic operations, or having defined some other methods). Once you use such properties, Luna typechecker automatically keeps track of them and checks whether they are satisfied.
class Vector a: x y z :: a def dotProduct that: self.x * that.x + self.y * that.y + self.z * that.z
dotProduct method will work with any elements supporting addition and multiplication, so using it with
Reals is fine, while using it with
Text results in a type error.
Vector 1 2 3 . dotProduct (Vector 4 5 6) # returns 32 :: Int Vector 1.0 2.0 3.0 . dotProduct (Vector 4.0 5.0 6.0) # returns 32.0 :: Real Vector "hello" "world" "!" . dotProduct (Vector "foo" "bar" "baz") # does not compile