Is there a reason why it is not possible to implement generic methods on a interface implementation?
type IMap =
abstract member Map: 'a -> 'b
type MapIntString() =
interface IMap with
member this.Map(x:int): string = sprintf "%i" x
type MapStringToInt() =
interface IMap with
member this.Map(x:string): int = 0I know I can
type IMap<'a, 'b> =
abstract member Map: 'a -> 'b
type MapIntString() =
interface IMap<int, string> with
member this.Map x = sprintf "%i" x
type MapStringToInt() =
interface Map<string, int> with
member this.Map (x:string): int = 0But that is not always possible or leads enormous amounts of code.
for example
type MapFoo(f: 'a -> 'b) =
interface Map with
member this.Map (x:Foo<'a>): Foo<'b> =
let (Foo a) = x
Foo (f a)In the above example at the moment I would have to create a specialized impl for any combination of 'a and 'b of Foo<_> whereas with an implementation like MapFoo I just need the functions that do the conversion and give one of these functions during construction time
So my question is: are there any hard technical limitations (CLR/.NET) or type theory or type inferrence that prevents this? And if so why is it even possible to define the interface like
type IMap =
abstract member Map: 'a -> 'bWhy not have a compiler error when trying to define a generic abstract method that uses generic types that are not defined on the type itself?
.exe anywhere,