Extension methods for specific generic types

Question

I'm attempting to create various extension method for a generic type bound to specific generic type parameters in F#, but the language does not seem to be allowing me:

What I want to do is something like the following:

type IEnumerable<int> with
    member this.foo =
        this.ToString()

Yet it gives me the compiler error (underlining the int keyword):

Unexpected identifier in type name. Expected infix operator, quote symbol or other token.

The following does work, though it does not specifically bind the generic type parameter to int, as I want:

type IEnumerable<'a> with
    member this.foo =
        this.ToString()

Is there any way to accomplish this aim in F# - am I perhaps just using the wrong syntax? If not, I would appreciate if someone could suggest a workaround, perhaps using type constraints somewhere.

Answer 1

Well, you can use constraints - but not with sealed types like int.

type IEnumerable<'a when 'a :> InheritableType> =
member this.Blah =
    this.ToString()

Hmm...

Answer 2

This isn't possible in the current version of F#, unfortunately. See related question here.