type array<'t, 'ndims> =
    {
        nrows : int
        ncols : int
    }

type ndims2 =
    static member index (a:array<_, ndims2>) =
        let indexImpl (i:int, j:int) = i + j*a.nrows
        indexImpl

let inline indexer (a:array<_, 'ndims>) =
    (^ndims : (static member index : array<_, ^ndims> -> _) a)

let x : array<float, ndims2> = {nrows = 2; ncols = 2}
let i = indexer x