Question

I made a function in F#

let tryParseArray tryParse (separator:char) (line: string) =
    // inside the function I use the tuple form of tryParse

It works fine if I call it in such way: tryParseArray Int32.TryParse ',' "2,3,2,3,2"

Now I would like this function to be available in C# as well, so I did this:

static member TryParseArray (line, tryParse, separator) =
    line |> tryParseArray tryParse separator

Then I realized that TryParseArray actually takes tryParse argument as FSharpFunc, which is not friendly to C# at all, so I tried this:

static member TryParseArray (line, [<Out>] tryParse: (string * byref<'a> -> bool), separator) =
    line |> tryParseArray tryParse separator

but now tryParseArray doesn’t accept tryParse as a valid argument (type error)

What should I do?

I wish in C# I can call TryParseArray("2,3,2,3,2", Int32.TryParse, ',') as well

Answer 1

You can expose this function to C# using custom delegate type :

EDITED

// F#
module Lib

let tryParseArray parser (line : string) (sep : char) = 
    // don't know your exact implementation so again just guessing...
    line.Split sep
    |> Array.choose (fun el ->
        match parser el with
        | true, el -> Some el
        | false, _ -> None
        )

open System.Runtime.InteropServices
type TryParse<'R>  = delegate of str : string * [<Out>] res : byref<'R> -> bool

type T = 
    static member TryParse(line : string, tryParse : TryParse<'R>, separator : char) : 'R[] = 
        tryParseArray tryParse.Invoke line separator


 //C# 
 var r = Lib.T.TryParse<int>("1,2,3", int.TryParse, ',');

NOTE: on the C# side you’ll need to specify type parameter for TryParse explicitly (Why don’t anonymous delegates/lambdas infer types on out/ref parameters?)