Question

If you were to define some extension methods, properties in an assembly written in F#, and then use that assembly in C#, would you see the defined extensions in C#?

If so, that would be so cool.

Answer 1

[<System.Runtime.CompilerServices.Extension>]
module Methods =   
    [<System.Runtime.CompilerServices.Extension>]   
    let Exists(opt : string option) =                
    match opt with
       | Some _ -> true                  
       | None -> false

This method could be used in C# only by adding the namespace (using using) to the file where it will be used.

if (p2.Description.Exists()) {   ...}

Here is a link to the original blogpost.

Answering question in comments “Extension Static Methods”:

namespace ExtensionFSharp 

module CollectionExtensions = 

  type System.Linq.Enumerable with   
    static member RangeChar(first:char, last:char) = 
      {first .. last}

In F# you call it like so:

open System.Linq 
open ExtensionFSharp.CollectionExtensions 

let rangeChar = Enumerable.RangeChar('a', 'z') 
printfn "Contains %i items" rangeChar.CountItems

In C# you call it like so:

using System;
using System.Collections.Generic;
using ExtensionFSharp;

    class Program
    {
        static void Main(string[] args)
        {
            var method = typeof (CollectionExtensions).GetMethod("Enumerable.RangeChar.2.static");


            var rangeChar = (IEnumerable<char>) method.Invoke(null, new object[] {'a', 'z'});
            foreach (var c in rangeChar)
            {
                Console.WriteLine(c);
            }
        }
    }

Now, give me my freaking medal!