Rust and .NET, both directions

src/lib.rs (edit me)

Native.cs (generated: 4 functions)

// <auto-generated> by Rust Studio from the extern "C" functions in lib.rs
using System;
using System.Runtime.InteropServices;

namespace MathLib;

public static class Native
{
    private const string Lib = "mathlib";

    [DllImport(Lib, EntryPoint = "add", CallingConvention = CallingConvention.Cdecl)]
    private static extern int add_raw(int a, int b);
    public static int Add(int a, int b) => add_raw(a, b);

    [DllImport(Lib, EntryPoint = "scale", CallingConvention = CallingConvention.Cdecl)]
    private static extern double scale_raw(double x, double factor);
    public static double Scale(double x, double factor) => scale_raw(x, factor);

    // string arguments are marshalled as UTF-8
    [DllImport(Lib, EntryPoint = "greet", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
    private static extern IntPtr greet_raw([MarshalAs(UnmanagedType.LPUTF8Str)] string name);
    public static string Greet(string name)
    {
        var p = greet_raw(name);
        try { return Marshal.PtrToStringUTF8(p)!; } finally { FreeString(p); }
    }

    [DllImport(Lib, EntryPoint = "free_string", CallingConvention = CallingConvention.Cdecl)]
    private static extern void free_string_raw(IntPtr s);
    private static void FreeString(IntPtr p) => free_string_raw(p);
}

Package contents

MathLib.0.1.0.nupkg
├─ MathLib.nuspec
├─ contentFiles/cs/any/Native.cs      (the generated wrapper, compiled into the consumer)
├─ runtimes/win-x64/native/mathlib.dll
└─ [Content_Types].xml

In a C# project

dotnet add package MathLib --version 0.1.0 --source ./nupkg

Console.WriteLine(Native.Add(2, 3)); // 5