F# create instance method for a constrained generic parameter - f#

Question

Is it possible to have an instance method of a class which only works when the generic type is restricted to a particular type?
For example, I want to define an Add method which only works when the contained type is float. Here's the closest I've gotten but I'm unsure how to constrain the 'Value type to float in the member _.Add signature. Right now I get an error on the next to the last line saying the type of 'Value cannot be resolved at compile time. Can I restrict this method to only apply when the type of 'Value is float?
type ImArr<[<Measure>] 'Index, 'Value>(values: array<'Value>) =
// We want to make sure we have our own copy to protect against mutation
let values = values |> Array.copy
member internal _.Values : array<'Value> = values
member this.Item
with get(index: int<'Index>) =
values.[int index]
type Arr<[<Measure>] 'Index, 'Value>(values: array<'Value>) =
// We want to make sure we have our own copy to protect against mutation
let values = values |> Array.copy
member this.Item
with get(index: int<'Index>) =
values.[int index]
and set(index: int<'Index>) (value: 'Value) =
values.[int index] <- value
member internal _.Values : array<'Value> = values
// This is the method I would like to constrain to only be used when the
// type of 'Value is float
member _.Add (b: ImArr<'Index, float>) =
if values.Length <> b.Values.Length then
invalidArg (nameof b) "Cannot add arrays of different lengths"
// TODO: Turn this into something using SIMD intrinsics
let mutable i = 0
while i < values.Length && i < b.Values.Length do
values.[i] <- values.[i] + b.Values.[i] // <-- Error here
i <- i + 1

Answer 1

As mentioned by #brianberns in the comments, not directly. However, C#-style extension methods can be defined for a specialized version of a class. The caveat is that as an extension method, it won't have access to private members.
[<Extension>]
type ArrExtensions =
[<Extension>]
static member Add (this: ImArr<'Index, float>, b: ImArr<'Index, float>) =
if this.Values.Length <> b.Values.Length then
invalidArg (nameof b) "Cannot add arrays of different lengths"
// TODO: Turn this into something using SIMD intrinsics
let mutable i = 0
while i < this.Values.Length && i < b.Values.Length do
this.Values.[i] <- this.Values.[i] + b.Values.[i] // <-- Error here
i <- i + 1
// When the namespace containing the above type is opened,
// the following can be called:
floatArr1.Add(floatArr2)