Question

I have a c# dll library with one method g accepting the following function f in C# as an input

 void f(double[] x, ref double func, double[] grad, object obj)

In the function body, both func and grad values are updated. The input signature of g(f) in F# reads

f:float[]-> byref<float> -> float[]-> obj->unit

how can I write f in f# to use g(f) in f#?

EDIT when I follow ildjarn’s answer below like

let f(x:float[]) (func:byref<float>) (grad:float[]) (obj: obj) = 
    func <- ...
    grad.[0] <- ... 
    grad.[1] <- ...
    ...
    ()

I got error on g(f) with

This function value is being used to construct a delegate type whose signature includes a byref argument. You must use an explicit lambda expression taking 4 arguments.

what should I do to make it work? thanks.
UPDATE: it turns out I have to use g(fun (x:float[]) (func:byref<float>) (grad:float[]) (obj: obj) -> .... Cannot give the inside function a name like f.

Answer 1

let function1 (x:double[], func:byref<double>, grad:double[], obj:obj) = ...