Cannot implement a generic interface with static abstract members with different generic arguments

[Andreas-Dorfer]

I'm experimenting with the new System.Numerics namespace and came across an issue with generic interfaces with static abstract members. I cannot implement a generic interface with static abstract members with different generic arguments. In this example, I want to implement IMultiplyOperators<Vector, double, Vector> and IMultiplyOperators<Vector, Vector, Vector>.

open System.Numerics

type Vector = Vector of x: double * y: double * z: double with

    //factor
    static member (*) (Vector (x, y, z), f) =
        Vector (x * f, y * f, z * f)

    //cross product
    static member (*) (Vector (x1, y1, z1), Vector (x2, y2, z2)) =
        Vector (y1 * z2 - z1 * y2, z1 * x2 - x1 * z2, x1 * y2 - y1 * x2)

    interface IMultiplyOperators<Vector, double, Vector> with
        static member (*) (a, f) = a * f
    interface IMultiplyOperators<Vector, Vector, Vector> with
        static member (*) (a, b) = a * b

I'm getting the following compiler errors:

Program.fs(13,15): error FS0001: This expression was expected to have type    'decimal'    but here has type    'Vector'
Program.fs(13,15): error FS0001: This expression was expected to have type    'decimal'    but here has type    'Vector'
Program.fs(13,15): error FS0909: All implemented interfaces should be declared on the initial declaration of the type

• net7.0
• FSharp.Core 7.0.300
• Visual Studio 17.6.5
• MSBuild version 17.6.8+c70978d4d for .NET

VectorTry.zip

[vzarytovskii]

It is supported for instance members, not sure what's the issue with statics: https://github.com/fsharp/fslang-suggestions/issues/545

[edgarfgp]

@gusty will this also be fixed by https://github.com/dotnet/fsharp/pull/16199 ?

[gusty]

No @edgarfgp , #16199 is about allowing 'interface .. with' within an interface, in this case is a type which is already supported.

Program.fs(13,15): error FS0909: All implemented interfaces should be declared on the initial declaration of the type is already solved in F#8 by #16157

However if I find time I could have a look and see where the issue is, in the compiler.

[edgarfgp]

Thanks for the clarification. Happy to work together on this if do not have much time