int64 doesn't support LanguagePrimitives.DivideByInt?

Question

Why int64 doesn't support LanguagePrimitives.DivideByInt? I thought it would be pretty natural to write something like this:

let inline DivBy2 n = LanguagePrimitives.DivideByInt n 2
let res = DivBy2 100L

But compiler says that int64 doesn't support the operator DivideByInt.

I've tried to cheat with:

type System.Int64 with 
    static member DivideByInt (n: System.Int64) (d: int) = n / (int64 d)

But it doesn't work.

What can be done to perform generic division of int64 by int?

Answer 1

Looking at the F# source code, the type int64 is not included in the function DivideByInt, I don't know why.

You can defining another generic function like this:

open LanguagePrimitives
type DivExtension = DivExtension of int with
    static member inline (=>) (x             , DivExtension y) = DivideByInt x y
    static member        (=>) (x:int64       , DivExtension y) = x / (int64 y)
    static member        (=>) (x:DivExtension, DivExtension y) = x

let inline DivByInt x y = x => DivExtension y

Or you can even shadow the original DivideByInt function:

let inline DivideByInt x y = x => DivExtension y

Note you can also add more overloads (ie for int), in which case you don't need the last "dummy" overload to infer the right signature.