Is it possible to write `justAddThem1` such that it takes an

Question

Is it possible to write `justAddThem1` such that it takes any numeric type `justAddThem2` and `justAddThem3` won t compile ``` fun justAddThem1 x Int y Int = x + y fun justAddThem2 x Number y Number = x + y fun lt T Number gt justAddThem3 x T y T = x + y ```

Andreas Sinz · Answer

use ad hoc polymorphism <http beust com weblog 2016 06 20 ad hoc polymorphism in kotlin >

Andreas Sinz · Answer

e g `fun lt T Number gt justAddThem x T y T f T T gt T = f x y `

Can Orhan · Answer

Thanks < Andreas Sinz> Didn t know that was the term for it smile

Andreas Sinz · Answer

< Can Orhan> thats how < cedric> calls it grimacing

Can Orhan · Answer

Good enough for me smile

cedric · Answer

Hopefully it s not just me calling it that slightly smiling face

lifter · Answer

I actually know Haskell and am familiar with the terms ad hoc polymorphism and the other side of the coin parametric polymorphism Parametric polymorphism is when you re dealing with a type that could be absolutely anything under the sun So if I were to attempt to apply the term to Kotlin I d imagine something like this

lifter · Answer

``` fun lt T gt f x T ``` Function `f` is parametrically polymorphic Ad hoc polymorphism in Haskell would be when there is a typeclass constraint on the type variable Haskell typeclasses are similar to OOP interfaces So in Kotlin I d imagine something like this ``` fun lt T Comparable gt f x T ```

lifter · Answer

`T` is constrained in the sense that it s no longer anything under the sun it s anything that is comparable

cedric · Answer

< jason> I wouldn t call type boundaries ad hoc polymorphism they are a different concept Ad hoc polymorphism is more concerned with adjusting types to make them conform to an interface they do not initially conform with

lifter · Answer

OK

lifter · Answer

Well I m only familiar with how the terms apply to Haskell

lifter · Answer

In any case this ``` fun lt T Number gt justAddThem x T y T f T T gt T = f x y ``` really doesn t add the numbers does it Looks like it just takes two numbers and a function and applies the function to the two numbers

cedric · Answer

Yes I guess it s a more universal add in a monoidal sense Combine would be another term

lifter · Answer

I think it s just function application `f` could do anything

lifter · Answer

It could for example just perform a side effect perhaps ``` fun f x Int y Int println $x $y ```

lifter · Answer

I guess my point is maybe one s intent is to use `justAddThem` to add or combine in some sense but there are no guarantees from the type system or otherwise that enforce that

Andreas Sinz · Answer

< lifter> thats a typesafe way to do it you could also do it the following way e g ``` fun lt T Number gt justAddThem x T y T T return when x is Int amp amp y is Int gt x + y x is Double amp amp y is Double gt x + y else gt throw Exception as T ```

lifter · Answer

OK I can see that Though personally I m not a big fan of all the boilerplate I wonder if it would work without the ` amp amp y is Int` if `x` and `y` are both `T`

Andreas Sinz · Answer

sadly it doesn t right now