[ENH] Add LuaObject(UserData)

[JenyaRostov]

Description

I want to add easy UserData support to GmodDotNet

LuaObject is a inheritable class that allows to push and pop c#-style userdata. It already implements some basic metamethods such as __gc and __tostring, with virtual methods Destroy and Name for child classes to override.
At the module startup, every class inherited from LuaObject and with [UserData(string Name)] attribute would be registered.
Registering luaobject consists of steps:

1. Create metatable using lua.CreateMetatable using name from [UserData] attribute
2. Write TypeName, TypeId from CreateMetaTable and Type to internal Dictionary
3. Get all static methods with signature int (ILua lua) and [MetaMethod] attribute from the class and push them as metamethods
4. Create table and push all static methods with the same signature but without [MetaMethod] attribute
5. Make new table an __index for metatable

Usage

Creating LuaObject

    [UserData(Name = "MyLuaObject")]
    public class MyLuaObject : LuaObject<MyLuaObject>
    {
        public override string Name() => "MyLuaObject";
        public override void Destroy() => Console.WriteLine("Garbage collected!");
        public int SomeInt = 5;
        private static int ReturnNumber(ILua lua)
        {
            var self = Pop(lua);
            lua.PushNumber(self.SomeInt);
            return 1;
        }
    }

Pushing and poping

    int SomePushLuaMethod(ILua lua)
    {
        MyLuaObject obj = new MyLuaObject();
        obj.Push(lua);
        return 1;
    }
    int SomePopLuaMethod(ILua lua)
    {
        MyLuaObject obj = MyLuaObject.Pop(1); // Pop first argument
        Console.WriteLine(obj.SomeInt);
    }

Usage in lua is as follows:

    local myObj = SomePushLuaMethod()
    print(myObj:ReturnNumber())
    SomePopLuaMethod(myObj) -- 5 in console
    myObj = nil --__gc would be called, also calling Destroy virtual method

[luttje]

I'm working on something very similar. With me instead of manually manipulating the Lua stack I convert between Lua and .NET objects.

An example:

[LuaMethod]
public List<MongoDB.Bson.BsonDocument> Find(MongoBsonDocument filter)
{
        var results = collection.Find(filter.BsonDocument);

        return results.ToList();
}

Called like this in Lua

local filter = { _id = "singleplayer" }
local results = collection:Find(filter) -- collection is a MongoDB collection userdata
PrintTable(results)

Transformers handle converting the types automatically.

In the image below you can see how the returned value by Find is converted to Lua (I'm in the middle of refactoring and adding support for method overloading, so the code below I'll likely simplify).

I think my BindingHelper.GenerateUserDataFromObject is kind of what you are describing. Once I'm satisfied with where I'm at I'll set my repo to public and share it here so you can have a look.

In the meanwhile I'll attach a couple files which are heavily under construction, but should give an idea how I'm approaching this atm.

Binding.zip

[JenyaRostov]

Oh yeah, that's way better

[luttje]

I'm not sure it's better, but it's a different approach. Thanks anyway.

I'm not done yet and certainly not happy about the code, but decided to make my project repo public so you can have a look.

I intend to eventually extract the whole GmodMongoDb.Binding namespace into a NuGet package. It seems like a cool utility that I think would be nice to have, but not necessarily something that should become a PR for GmodNET. Mostly because of the expensive reflections that I haven't even begun to think of optimizing yet.

I'm very much open to suggestions and critique. The issues on my repo is the best place for that I think.

[GlebChili]

@JenyaRostov I really like your idea, but I have several considerations against shipping it as a part of core GmodDotNet. GmodDotNet by itself is a low level wrapper for Gmod API and should update slowly and contain only minimum functionality. What we can do instead is to ship it as an additional NuGet package, something like GmodNET.Extensions. It will contain helper methods and classes for developers. Keeping it in separate repo and distributing it as separate nuget package will allow as to update it independently of GmodDotNet runtime and make it more flexible to maintain. What do you think?

[luttje]

Good idea @GlebChili!

If you want you can use the code I currently have in my GmodMongoDb.Binding namespace in the before mentioned repo.

I'll keep working on my code to make it more stable and concise, so it would be a good starting point candidate for the proposed Extensions package.

[JenyaRostov]

Yes, i think that's a good idea @GlebChili!
Although now we need to decide what solution to implement....

[luttje]

No need for a hard decision. I'll keep working on my solution, so it'll always be an option. Regardless of the package it'll find a home in or what other packages may appear.

If you feel like writing your own extension I do encourage you to do so. It's a lot of fun to be working with Gmod.NET and .NET Attributes in this way

[luttje]

Since it's been 27 days I feel obliged to inform y'all that I've been distracted from working on my prototype of an extensions wrapper. I may continue working on it in a week or so when I've got time free from work.