Importing Nim modules from C#

ImportNim.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace nim_sharp
{
    [StructLayout(LayoutKind.Sequential)]
    public unsafe struct NimSring
    {
        public Int32 Len;
        public Int32 Capacity;
        public char Text;
    }

    [StructLayout(LayoutKind.Sequential)]
    public unsafe struct NimSeq
    {
        public Int32 Len;
        public Int32 Capacity;
        public byte Data;
    }

    [StructLayout(LayoutKind.Sequential)]
    public unsafe struct NimType_ext
    {
        public Int32 x;
        public Int32 y;
        public NimSring* s;
    }

    public struct NimType
    {
        public int x;
        public int y;
        public string s;
    }

    class Program
    {
        [DllImport("nimlib.dll", CallingConvention = CallingConvention.Cdecl)]
        public static unsafe extern void populateArraySruct(int length, NimSeq** ArrayStructs);
 
        public static unsafe List<NimType> getResultsFromNim(int ArrL)
        {
            List<NimType> convertedResults = new List<NimType>(ArrL);
            
            NimSeq* nimResults = null;
            populateArraySruct(ArrL, &nimResults);
            
            NimType_ext* currentItem = (NimType_ext*) &(nimResults->Data);
            for (int i = 0; i < ArrL; i++, currentItem++)
            {
                convertedResults.Add(new NimType() {x = currentItem->x, y = currentItem->y, s = new string(&(currentItem->s->Text))});
            }
            return convertedResults;
        }

        static void Main(string[] args)
        {
            var list = getResultsFromNim(10);

            foreach (var elem in list) {
                Console.WriteLine("x: {0}, y: {1}, s: {2}", elem.x, elem.y, elem.s);
            }
        }
    }
}

nimlib.nim

# compile with nim c -app:lib nimlib.nim
# place next to the C# executable together with a compiled copy of nimrtl.dll

type
  NimTypeSeq = seq[NimType]
  NimType = object {.packed.}
    x: int
    y: int
    s: string
 
proc populateArraySruct(outputLength: int, output: var NimTypeSeq) {.exportc,dynlib.} =
  setupForeignThreadGc()

  output.newSeq(outputLength)
  
  for i in 0 .. <outputLength:
    output[i] = NimType(x: i, y: i*2, s: $i)
    

the only problem i have left as i mention in former post, as we only pass numeric char now it does work but encoding is wrong shows string as??? is this an issue or simple solution ? try concat $i as s= "abc" & $i

Nim strings are usually stored in UTF-8, although the language doesn't require that. In C#, the encoding is UCS-2 (UTF-16). Take a look at the following stackoverflow answer that features some conversion code:
http://stackoverflow.com/questions/10773440/conversion-in-net-native-utf-8-managed-string

StringFromNativeUtf8 is the one i think, i will take a time to test both ways to see if that is the solution, as this has to be the one, i will report to you as soon as i find the time to play with it again, thanks i think that concludes the subject of the string passing from nim to c# which was not a simple task for me, as soon as i will confront this, and do some more tests i will be more familiar and it will be simpler from that point, i'll let you know. thanks a lot as ususall !