MochiSharp

MochiSharp is a high-performance .NET hosting framework for C++ applications. It leverages the modern hostfxr API to provide a seamless, ultra-fast bridge between native C++ engines and C# script assemblies.

Designed for game engines and performance-critical applications, MochiSharp allows developers to use C# as a powerful scripting layer while maintaining native-level performance and flexibility.

Key Features

• Modern .NET Hosting: Built on the official hostfxr hosting API, supporting .NET 6, 7, 8, and beyond.
• High-Performance Interop: Uses [UnmanagedCallersOnly] for "Reverse P/Invoke," minimizing overhead when calling from C++ to C#.
• Hot-Reload Support: Leverages AssemblyLoadContext to allow unloading and reloading of script assemblies at runtime without restarting the application.
• Flexible Method Binding: Easily bind C++ function calls to C# instance or static methods using a robust signature-based system.
• Automated Type Discovery: Find and instantiate all classes deriving from a specific base type (e.g., GameScript) within a loaded assembly.
• Primitive & Struct Support: Efficiently pass integers, floats, booleans, and complex Sequential structs between native and managed code.

Architecture

MochiSharp consists of two primary components that handle the bridge between native and managed code:

graph TD
    A[C++ Application] -->|Uses| B[MochiSharp.Native]
    B -->|Calls hostfxr| C[ .NET Runtime ]
    C -->|Loads| D[MochiSharp.Managed]
    D -->|Manages| E[ScriptContext]
    E -->|Loads/Reloads| F[User Script Assemblies]
    F -->|Callback| B

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• MochiSharp.Native: A C++ static library that encapsulates the hosting logic, initialization, and method invocation.
• MochiSharp.Managed: The C# core library that acts as the internal bridge, managing collectible assembly contexts and type marshaling.

Getting Started

1. Scripting (C#)

Define your script classes in a separate C# project. You can use a common base class for easy discovery.

namespace MyGame.Scripts;

public class Player : GameScript
{
    private Transform _transform;

    public void OnUpdate(float deltaTime)
    {
        // Script logic here
    }
}

2. Hosting (C++)

Initialize the host and load your compiled script assembly.

#include "MochiSharp/Host.h"

MochiSharp::DotNetHost host;

// 1. Initialize with your runtime config
if (host.Init(L"MyGame.runtimeconfig.json")) {
    
    // 2. Load your script DLL
    host.LoadAssembly("Scripts.dll");

    // 3. Create an instance of a script class
    uint64_t instanceId = 1;
    host.CreateInstance("MyGame.Scripts.Player", instanceId);

    // 4. Bind and Invoke a method
    int updateMethod = host.BindInstanceMethod(instanceId, "OnUpdate", SIG_VOID_FLOAT);
    float dt = 0.16f;
    void* args[] = { &dt };
    host.Invoke(updateMethod, args, 1, nullptr);
}

Building the Project

MochiSharp uses standard CMake/Premake flows for the native side and the .NET CLI for the managed side.

1. Build Managed Core:

   dotnet build MochiSharp.Managed/MochiSharp.Managed.csproj -c Release

2. Build Native Library: Use your preferred build system (Visual Studio, Make, Ninja) to compile the C++ source in MochiSharp.Native.
3. Run the Example: See the Example/ directory for a complete working host and script implementation.